Unfortunately, Firefox does not support the `keepalive` parameter
I used in the previous PR. However it supports the `navigator.sendBeacon`
API that allows that kind of things, but does not allow setting headers.

Therefore, this PR replaces it with a `sendBeacon` call that passes the
bearer token in the POST data.

Doorkeeper will then handle the auth token out of the box, as long as
it is passed as form data. Passing the query as JSON does not work.

* Periodically save timeline markers

This saves timeline markers immediately upon message arrival, but not more
than once every 5 minutes.

This does not change how the markers are saved on closing the window,
except that it avoids submitting them if there is no need for it.

* Use the Fetch API when possible instead of XHR on window unload

Bumps [kaminari](https://github.com/kaminari/kaminari) from 1.2.0 to 1.2.1. **This update includes a security fix.**
- [Release notes](https://github.com/kaminari/kaminari/releases)
- [Changelog](https://github.com/kaminari/kaminari/blob/master/CHANGELOG.md)
- [Commits](https://github.com/kaminari/kaminari/compare/v1.2.0...v1.2.1)

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Bumps [is-promise](https://github.com/then/is-promise) from 2.1.0 to 2.2.2.
- [Release notes](https://github.com/then/is-promise/releases)
- [Commits](https://github.com/then/is-promise/compare/v2.1.0...2.2.2)

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Bumps [react-transition-group](https://github.com/reactjs/react-transition-group) from 2.5.2 to 2.9.0.
- [Release notes](https://github.com/reactjs/react-transition-group/releases)
- [Changelog](https://github.com/reactjs/react-transition-group/blob/master/CHANGELOG.md)
- [Commits](https://github.com/reactjs/react-transition-group/compare/v2.5.2...v2.9.0)

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Bumps [eslint-import-resolver-node](https://github.com/benmosher/eslint-plugin-import) from 0.3.2 to 0.3.3.
- [Release notes](https://github.com/benmosher/eslint-plugin-import/releases)
- [Changelog](https://github.com/benmosher/eslint-plugin-import/blob/master/CHANGELOG.md)
- [Commits](https://github.com/benmosher/eslint-plugin-import/compare/v0.3.2...resolvers/node/v0.3.3)

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Bumps [spdx-correct](https://github.com/jslicense/spdx-correct.js) from 3.1.0 to 3.1.1.
- [Release notes](https://github.com/jslicense/spdx-correct.js/releases)
- [Commits](https://github.com/jslicense/spdx-correct.js/compare/v3.1.0...v3.1.1)

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Bumps [yaml](https://github.com/eemeli/yaml) from 1.9.2 to 1.10.0.
- [Release notes](https://github.com/eemeli/yaml/releases)
- [Commits](https://github.com/eemeli/yaml/compare/v1.9.2...v1.10.0)

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Bumps [watchpack](https://github.com/webpack/watchpack) from 1.6.1 to 1.7.2.
- [Release notes](https://github.com/webpack/watchpack/releases)
- [Commits](https://github.com/webpack/watchpack/compare/v1.6.1...v1.7.2)

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Bumps [node-releases](https://github.com/chicoxyzzy/node-releases) from 1.1.55 to 1.1.56.
- [Release notes](https://github.com/chicoxyzzy/node-releases/releases)
- [Commits](https://github.com/chicoxyzzy/node-releases/compare/v1.1.55...v1.1.56)

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Bumps [compression-webpack-plugin](https://github.com/webpack-contrib/compression-webpack-plugin) from 3.1.0 to 4.0.0.
- [Release notes](https://github.com/webpack-contrib/compression-webpack-plugin/releases)
- [Changelog](https://github.com/webpack-contrib/compression-webpack-plugin/blob/master/CHANGELOG.md)
- [Commits](https://github.com/webpack-contrib/compression-webpack-plugin/compare/v3.1.0...v4.0.0)

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Bumps [tesseract.js](https://github.com/naptha/tesseract.js) from 2.0.0-alpha.16 to 2.1.1.
- [Release notes](https://github.com/naptha/tesseract.js/releases)
- [Commits](https://github.com/naptha/tesseract.js/compare/v2.0.0-alpha.16...v2.1.1)

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Bumps [jsx-ast-utils](https://github.com/evcohen/jsx-ast-utils) from 2.2.3 to 2.3.0.
- [Release notes](https://github.com/evcohen/jsx-ast-utils/releases)
- [Changelog](https://github.com/jsx-eslint/jsx-ast-utils/blob/master/CHANGELOG.md)
- [Commits](https://github.com/evcohen/jsx-ast-utils/compare/2.2.3...2.3.0)

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Bumps [memoize-one](https://github.com/alexreardon/memoize-one) from 5.0.4 to 5.1.1.
- [Release notes](https://github.com/alexreardon/memoize-one/releases)
- [Commits](https://github.com/alexreardon/memoize-one/compare/v5.0.4...v5.1.1)

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Bumps [jest-leak-detector](https://github.com/facebook/jest/tree/HEAD/packages/jest-leak-detector) from 25.4.0 to 25.5.0.
- [Release notes](https://github.com/facebook/jest/releases)
- [Changelog](https://github.com/facebook/jest/blob/master/CHANGELOG.md)
- [Commits](https://github.com/facebook/jest/commits/v25.5.0/packages/jest-leak-detector)

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Bumps [browserify-sign](https://github.com/crypto-browserify/browserify-sign) from 4.1.0 to 4.2.0.
- [Release notes](https://github.com/crypto-browserify/browserify-sign/releases)
- [Commits](https://github.com/crypto-browserify/browserify-sign/compare/v4.1.0...v4.2.0)

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Bumps [events](https://github.com/Gozala/events) from 3.0.0 to 3.1.0.
- [Release notes](https://github.com/Gozala/events/releases)
- [Changelog](https://github.com/Gozala/events/blob/master/History.md)
- [Commits](https://github.com/Gozala/events/compare/v3.0.0...v3.1.0)

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Bumps [yargs-parser](https://github.com/yargs/yargs-parser) from 13.1.1 to 13.1.2.
- [Release notes](https://github.com/yargs/yargs-parser/releases)
- [Changelog](https://github.com/yargs/yargs-parser/blob/master/CHANGELOG.md)
- [Commits](https://github.com/yargs/yargs-parser/commits)

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Bumps [sass](https://github.com/sass/dart-sass) from 1.26.3 to 1.26.5.
- [Release notes](https://github.com/sass/dart-sass/releases)
- [Changelog](https://github.com/sass/dart-sass/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sass/dart-sass/compare/1.26.3...1.26.5)

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Bumps [css-loader](https://github.com/webpack-contrib/css-loader) from 3.4.2 to 3.5.3.
- [Release notes](https://github.com/webpack-contrib/css-loader/releases)
- [Changelog](https://github.com/webpack-contrib/css-loader/blob/master/CHANGELOG.md)
- [Commits](https://github.com/webpack-contrib/css-loader/compare/v3.4.2...v3.5.3)

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Bumps [external-editor](https://github.com/mrkmg/node-external-editor) from 3.0.3 to 3.1.0.
- [Release notes](https://github.com/mrkmg/node-external-editor/releases)
- [Changelog](https://github.com/mrkmg/node-external-editor/blob/master/.release.json)
- [Commits](https://github.com/mrkmg/node-external-editor/compare/3.0.3...3.1.0)

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Bumps [uuid](https://github.com/uuidjs/uuid) from 8.0.0 to 8.1.0.
- [Release notes](https://github.com/uuidjs/uuid/releases)
- [Changelog](https://github.com/uuidjs/uuid/blob/master/CHANGELOG.md)
- [Commits](https://github.com/uuidjs/uuid/compare/v8.0.0...v8.1.0)

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Bumps [rack-attack](https://github.com/kickstarter/rack-attack) from 6.3.0 to 6.3.1.
- [Release notes](https://github.com/kickstarter/rack-attack/releases)
- [Changelog](https://github.com/kickstarter/rack-attack/blob/master/CHANGELOG.md)
- [Commits](https://github.com/kickstarter/rack-attack/compare/v6.3.0...v6.3.1)

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Not sure why dependabot hasn't made a PR for this yet, but there is a new
version of wicg-inert, which does not try to dynamically insert styles
anymore when those styles already exist. This will get rid of some of the
CSP violation warnings we get since getting rid of 'unsafe-inline'.

Bumps [rubocop](https://github.com/rubocop-hq/rubocop) from 0.83.0 to 0.84.0.
- [Release notes](https://github.com/rubocop-hq/rubocop/releases)
- [Changelog](https://github.com/rubocop-hq/rubocop/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rubocop-hq/rubocop/compare/v0.83.0...v0.84.0)

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Bumps [sidekiq-unique-jobs](https://github.com/mhenrixon/sidekiq-unique-jobs) from 6.0.21 to 6.0.22.
- [Release notes](https://github.com/mhenrixon/sidekiq-unique-jobs/releases)
- [Changelog](https://github.com/mhenrixon/sidekiq-unique-jobs/blob/master/CHANGELOG.md)
- [Commits](https://github.com/mhenrixon/sidekiq-unique-jobs/compare/v6.0.21...v6.0.22)

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Bumps [aws-sdk-s3](https://github.com/aws/aws-sdk-ruby) from 1.64.0 to 1.66.0.
- [Release notes](https://github.com/aws/aws-sdk-ruby/releases)
- [Changelog](https://github.com/aws/aws-sdk-ruby/blob/master/gems/aws-sdk-s3/CHANGELOG.md)
- [Commits](https://github.com/aws/aws-sdk-ruby/compare/v1.64.0...v1.66.0)

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Bumps [pghero](https://github.com/ankane/pghero) from 2.4.2 to 2.5.0.
- [Release notes](https://github.com/ankane/pghero/releases)
- [Changelog](https://github.com/ankane/pghero/blob/master/CHANGELOG.md)
- [Commits](https://github.com/ankane/pghero/compare/v2.4.2...v2.5.0)

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Bumps [rails](https://github.com/rails/rails) from 5.2.4.2 to 5.2.4.3.
- [Release notes](https://github.com/rails/rails/releases)
- [Commits](https://github.com/rails/rails/compare/v5.2.4.2...v5.2.4.3)

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Bumps [puma](https://github.com/puma/puma) from 4.3.3 to 4.3.5.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](https://github.com/puma/puma/commits)

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Bumps [capybara](https://github.com/teamcapybara/capybara) from 3.32.1 to 3.32.2.
- [Release notes](https://github.com/teamcapybara/capybara/releases)
- [Changelog](https://github.com/teamcapybara/capybara/blob/master/History.md)
- [Commits](https://github.com/teamcapybara/capybara/compare/3.32.1...3.32.2)

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Bumps [electron-to-chromium](https://github.com/kilian/electron-to-chromium) from 1.3.432 to 1.3.448.
- [Release notes](https://github.com/kilian/electron-to-chromium/releases)
- [Changelog](https://github.com/Kilian/electron-to-chromium/blob/master/CHANGELOG.md)
- [Commits](https://github.com/kilian/electron-to-chromium/compare/v1.3.432...v1.3.448)

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Bumps [aws-sdk-core](https://github.com/aws/aws-sdk-ruby) from 3.95.0 to 3.96.1.
- [Release notes](https://github.com/aws/aws-sdk-ruby/releases)
- [Changelog](https://github.com/aws/aws-sdk-ruby/blob/master/gems/aws-sdk-core/CHANGELOG.md)
- [Commits](https://github.com/aws/aws-sdk-ruby/commits)

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Bumps [rspec-rails](https://github.com/rspec/rspec-rails) from 4.0.0 to 4.0.1.
- [Release notes](https://github.com/rspec/rspec-rails/releases)
- [Changelog](https://github.com/rspec/rspec-rails/blob/master/Changelog.md)
- [Commits](https://github.com/rspec/rspec-rails/compare/v4.0.0...v4.0.1)

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Bumps [compressible](https://github.com/jshttp/compressible) from 2.0.17 to 2.0.18.
- [Release notes](https://github.com/jshttp/compressible/releases)
- [Changelog](https://github.com/jshttp/compressible/blob/master/HISTORY.md)
- [Commits](https://github.com/jshttp/compressible/compare/v2.0.17...v2.0.18)

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Bumps [brakeman](https://github.com/presidentbeef/brakeman) from 4.8.1 to 4.8.2.
- [Release notes](https://github.com/presidentbeef/brakeman/releases)
- [Changelog](https://github.com/presidentbeef/brakeman/blob/master/CHANGES.md)
- [Commits](https://github.com/presidentbeef/brakeman/compare/v4.8.1...v4.8.2)

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Bumps [eslint-plugin-import](https://github.com/benmosher/eslint-plugin-import) from 2.20.1 to 2.20.2.
- [Release notes](https://github.com/benmosher/eslint-plugin-import/releases)
- [Changelog](https://github.com/benmosher/eslint-plugin-import/blob/master/CHANGELOG.md)
- [Commits](https://github.com/benmosher/eslint-plugin-import/compare/v2.20.1...v2.20.2)

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Bumps [tslib](https://github.com/Microsoft/tslib) from 1.11.2 to 1.13.0.
- [Release notes](https://github.com/Microsoft/tslib/releases)
- [Commits](https://github.com/Microsoft/tslib/compare/1.11.2...1.13.0)

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Bumps [caniuse-lite](https://github.com/ben-eb/caniuse-lite) from 1.0.30001041 to 1.0.30001061.
- [Release notes](https://github.com/ben-eb/caniuse-lite/releases)
- [Changelog](https://github.com/ben-eb/caniuse-lite/blob/master/CHANGELOG.md)
- [Commits](https://github.com/ben-eb/caniuse-lite/compare/v1.0.30001041...v1.0.30001061)

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Bumps [spdx-expression-parse](https://github.com/jslicense/spdx-expression-parse.js) from 3.0.0 to 3.0.1.
- [Release notes](https://github.com/jslicense/spdx-expression-parse.js/releases)
- [Commits](https://github.com/jslicense/spdx-expression-parse.js/compare/v3.0.0...v3.0.1)

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Bumps [jest-watcher](https://github.com/facebook/jest/tree/HEAD/packages/jest-watcher) from 25.4.0 to 25.5.0.
- [Release notes](https://github.com/facebook/jest/releases)
- [Changelog](https://github.com/facebook/jest/blob/master/CHANGELOG.md)
- [Commits](https://github.com/facebook/jest/commits/v25.5.0/packages/jest-watcher)

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Bumps [scroll-behavior](https://github.com/taion/scroll-behavior) from 0.9.9 to 0.9.12.
- [Release notes](https://github.com/taion/scroll-behavior/releases)
- [Commits](https://github.com/taion/scroll-behavior/compare/v0.9.9...v0.9.12)

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