This uses the same logic as the status icons in the glitch flavor.

Fixes #395

Instead of leaving the toot body blank, it replaces it with a single “.” in
order for the fold/unfold CW behavior to not look *too* weird on upstream
Mastodon. Note that this does not fix upstream's CW-dropping behavior, as
that is decided at the time the toot is posted, not received.

Indeed, when the “Always enable the Content Warning field” setting is enabled,
sending a content-less toot with a CW would move the CW to the toot's content
and leave the toot not marked as sensitive.

Fixes #783

Fixes #780

Fixes #778

Fixes #672

* Downcase signed_headers string before building the signed string

The HTTP Signatures draft does not mandate the “headers” field to be downcased,
but mandates the header field names to be downcased in the signed string, which
means that prior to this patch, Mastodon could fail to process signatures from
some compliant clients. It also means that it would not actually check the
Digest of non-compliant clients that wouldn't use a lowercased Digest field
name.

Thankfully, I don't know of any such client.

* Revert "Remove dead code (#8919)"

This reverts commit a00ce8c92c.

* Restore time window checking, change it to 12 hours

By checking the Date header, we can prevent replaying old vulnerable
signatures. The focus is to prevent replaying old vulnerable requests
from software that has been fixed in the meantime, so a somewhat long
window should be fine and accounts for timezone misconfiguration.

* Escape users' URLs when formatting them

Fixes possible HTML injection

* Escape all string interpolations in Formatter class

Slightly improve performance by reducing class allocations
from repeated Formatter#encode calls

* Fix code style issues

Merge upstream changes

Bumps [better_errors](https://github.com/BetterErrors/better_errors) from 2.4.0 to 2.5.0.
- [Release notes](https://github.com/BetterErrors/better_errors/releases)
- [Changelog](https://github.com/BetterErrors/better_errors/blob/master/CHANGELOG.md)
- [Commits](https://github.com/BetterErrors/better_errors/compare/v2.4.0...v2.5.0)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [bullet](https://github.com/flyerhzm/bullet) from 5.7.5 to 5.7.6.
- [Release notes](https://github.com/flyerhzm/bullet/releases)
- [Changelog](https://github.com/flyerhzm/bullet/blob/master/CHANGELOG.md)
- [Commits](https://github.com/flyerhzm/bullet/compare/5.7.5...5.7.6)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [scss_lint](https://github.com/brigade/scss-lint) from 0.57.0 to 0.57.1.
- [Release notes](https://github.com/brigade/scss-lint/releases)
- [Changelog](https://github.com/brigade/scss-lint/blob/master/CHANGELOG.md)
- [Commits](https://github.com/brigade/scss-lint/compare/v0.57.0...v0.57.1)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Fix #8685

Conflicts:
	app/javascript/packs/public.js

Changes made to app/javascript/packs/publics.js were applied to
app/javascript/core/settings.js

Bumps [capistrano-rails](https://github.com/capistrano/rails) from 1.3.1 to 1.4.0.
- [Release notes](https://github.com/capistrano/rails/releases)
- [Changelog](https://github.com/capistrano/rails/blob/master/CHANGELOG.md)
- [Commits](https://github.com/capistrano/rails/compare/v1.3.1...v1.4.0)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [dotenv-rails](https://github.com/bkeepers/dotenv) from 2.2.2 to 2.5.0.
- [Release notes](https://github.com/bkeepers/dotenv/releases)
- [Changelog](https://github.com/bkeepers/dotenv/blob/master/Changelog.md)
- [Commits](https://github.com/bkeepers/dotenv/compare/v2.2.2...v2.5.0)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Merge upstream changes

Bumps [faker](https://github.com/stympy/faker) from 1.8.7 to 1.9.1.
- [Release notes](https://github.com/stympy/faker/releases)
- [Changelog](https://github.com/stympy/faker/blob/master/CHANGELOG.md)
- [Commits](https://github.com/stympy/faker/compare/v1.8.7...v1.9.1)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [memory_profiler](https://github.com/SamSaffron/memory_profiler) from 0.9.11 to 0.9.12.
- [Release notes](https://github.com/SamSaffron/memory_profiler/releases)
- [Changelog](https://github.com/SamSaffron/memory_profiler/blob/master/CHANGELOG.md)
- [Commits](https://github.com/SamSaffron/memory_profiler/compare/v0.9.11...v0.9.12)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Merge upstream changes

* add ffmpeg initializer

* use different expression to check for environment var

Bumps [capybara](https://github.com/teamcapybara/capybara) from 3.8.2 to 3.9.0.
- [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/3.8.2...3.9.0)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [tty-prompt](https://github.com/piotrmurach/tty-prompt) from 0.17.0 to 0.17.1.
- [Release notes](https://github.com/piotrmurach/tty-prompt/releases)
- [Changelog](https://github.com/piotrmurach/tty-prompt/blob/master/CHANGELOG.md)
- [Commits](https://github.com/piotrmurach/tty-prompt/compare/v0.17.0...v0.17.1)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [aws-sdk-s3](https://github.com/aws/aws-sdk-ruby) from 1.20.0 to 1.21.0.
- [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/commits)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Bumps [i18n-tasks](https://github.com/glebm/i18n-tasks) from 0.9.21 to 0.9.25.
- [Release notes](https://github.com/glebm/i18n-tasks/releases)
- [Changelog](https://github.com/glebm/i18n-tasks/blob/master/CHANGES.md)
- [Commits](https://github.com/glebm/i18n-tasks/compare/v0.9.21...v0.9.25)

Signed-off-by: dependabot[bot] <support@dependabot.com>

* cleanup pass

* undo mistakes

* fixed.

* revert

SignatureVerification#matches_time_window? is not called anywhere.