Both of yarn and npm are used in Mastodon, but the combined usage requires
a redundant dependency and may lead to data inconsistency.

Considering that yarn has autoclean feature which npm does not have,
this change replaces all npm usage with yarn.

This change requires documentation update. Most notably, the following
command must be executed before assets precompilation if any system
dependency of node-sass has changed:

yarn install --force --pure-lockfile

* Specify AGPLv3+

Since the documentation doesn't specify you can use Mastodon as AGPLv3 or any later version.

* Use newest version of SPDX AGPLv3+ identifier

* Update babel-plugin-lodash to version 3.3.2

* Update enzyme to version 3.2.0

* Update enzyme-adapter-react-16 to version 1.1.0

* Update intersection-observer to version 0.5.0

* Update intl-messageformat to version 2.2.0

* Update node-sass to version 4.7.2

* Update postcss-loader to version 2.0.9

* Update React to version 16.2.0

* Update react-textarea-autosize to version 5.2.1

* Update stringz to version 0.3.0

* Update webpack to version 3.9.1

* Update webpack-bundle-analyzer to version 2.9.1

* Update webpack-dev-server to version 2.9.5

* Update webpack-merge to version 4.1.1

* Update fsevents to version 1.1.3

* yarn upgrade

* Update autoprefixer to version 7.1.6

* Update babel-plugin-preval to version 1.6.1

* Update babel-plugin-transform-react-remove-prop-types to version 0.4.10

* Update babel-preset-env to version 1.6.1

* Update cross-env to version 5.1.1

* Update enzyme-adapter-react-16 to version 1.0.2

* Update eslint-plugin-import to version 2.8.0

* Update immutable to version 3.8.2

* Update express to 4.16.2

* Update intl-relativeformat to version 2.1.0

* Update postcss-loader to version 2.0.8

* Update react-immutable-pure-component to version 1.1.1

* Update react-motion to version 0.5.2

* Update react-notification to version 6.8.2

* Update react-overlays to version 0.8.3

* Update react-redux-loading-bar to version 2.9.3

* Update resolve-url-loader to version 2.2.0

* Update style-loader to version 0.19.0

* Update webpack to version 3.8.1

* Update webpack-dev-server to version 2.9.3

* yarn upgrade

* Enable ESLint rules import/*

* fix

* Track frequently used emojis in web UI

* Persist emoji usage, but debounce commits to the settings API

* Fix #5144 - Add tooltips to picker

* Display only 2 lines of frequently used emojis

* Fix #2102 - Implement hotkeys

Hotkeys on status list:

- r to reply
- m to mention author
- f to favourite
- b to boost
- enter to open status
- p to open author's profile
- up or k to move up in the list
- down or j to move down in the list
- 1-9 to focus a status in one of the columns
- n to focus the compose textarea
- alt+n to start a brand new toot
- backspace to navigate back

* Add navigational hotkeys

The key g followed by:

- s: start
- h: home
- n: notifications
- l: local timeline
- t: federated timeline
- f: favourites
- u: own profile
- p: pinned toots
- b: blocked users
- m: muted users

* Add hotkey for focusing search, make escape un-focus compose/search

* Fix focusing notifications column, fix hotkeys in compose textarea

Fixes #5188

* Upgrade to React 16.0.0

* Disable some uncritical tests while chai-enzyme remains incompatible

* Remove react-sizeme

* Fix aspect ratio in "sensitive" mode

* In detail status view, display attachment uncropped if there's only one

* Make media spoiler the size of the media it hides, enable on static

* Switch from EmojiOne to Twemoji, different emoji picker

* Make emoji-mart use a local spritesheet

* Fix emojify test

* yarn manage:translations

* Make dropdowns render into portal, expand animation

* Improve actions modal style

* chore(yarn): Install detect-passive-events

* fix(column): Use passive listener

* chore(yarn): Install babel-plugin-preval as development dependency

* feat(babel): Add preval as a plugin

* feat(emojione_light): Prevaled module what tree-shaked emojione

* refactor(emoji): Use emojione_light

* feat: Preload emojione_picker bundle

* fix(emojione_light): Do not use Object.entries

* fix(emojify): Update tests

* chore(emojione_light): Remove silly ascii art

* feat: Register push subscription

* feat: Notify when mentioned

* feat: Boost, favourite, reply, follow, follow request

* feat: Notification interaction

* feat: Handle change of public key

* feat: Unsubscribe if things go wrong

* feat: Do not send normal notifications if push is enabled

* feat: Focus client if open

* refactor: Move push logic to WebPushSubscription

* feat: Better title and body

* feat: Localize messages

* chore: Fix lint errors

* feat: Settings

* refactor: Lazy load

* fix: Check if push settings exist

* feat: Device-based preferences

* refactor: Simplify logic

* refactor: Pull request feedback

* refactor: Pull request feedback

* refactor: Create /api/web/push_subscriptions endpoint

* feat: Spec PushSubscriptionController

* refactor: WebPushSubscription => Web::PushSubscription

* feat: Spec Web::PushSubscription

* feat: Display first media attachment

* feat: Support direction

* fix: Stuff broken while rebasing

* refactor: Integration with session activations

* refactor: Cleanup

* refactor: Simplify implementation

* feat: Set VAPID keys via environment

* chore: Comments

* fix: Crash when no alerts

* fix: Set VAPID keys in testing environment

* fix: Follow link

* feat: Notification actions

* fix: Delete previous subscription

* chore: Temporary logs

* refactor: Move migration to a later date

* fix: Fetch the correct session activation and misc bugs

* refactor: Move migration to a later date

* fix: Remove follow request (no notifications)

* feat: Send administrator contact to push service

* feat: Set time-to-live

* fix: Do not show sensitive images

* fix: Reducer crash in error handling

* feat: Add badge

* chore: Fix lint error

* fix: Checkbox label overlap

* fix: Check for payload support

* fix: Rename action "type" (crash in latest Chrome)

* feat: Action to expand notification

* fix: Lint errors

* fix: Unescape notification body

* fix: Do not allow boosting if the status is hidden

* feat: Add VAPID keys to the production sample environment

* fix: Strip HTML tags from status

* refactor: Better error messages

* refactor: Handle browser not implementing the VAPID protocol (Samsung Internet)

* fix: Error when target_status is nil

* fix: Handle lack of image

* fix: Delete reference to invalid subscriptions

* feat: Better error handling

* fix: Unescape HTML characters after tags are striped

* refactor: Simpify code

* fix: Modify to work with #4091

* Sort strings alphabetically

* i18n: Updated Polish translation

it annoys me that it's not fully localized :P

* refactor: Use current_session in PushSubscriptionController

* fix: Rebase mistake

* fix: Set cacheName to mastodon

* refactor: Pull request feedback

* refactor: Remove logging statements

* chore(yarn): Fix conflicts with master

* chore(yarn): Copy latest from master

* chore(yarn): Readd offline-plugin

* refactor: Use save! and update!

* refactor: Send notifications async

* fix: Allow retry when push fails

* fix: Save track for failed pushes

* fix: Minify sw.js

* fix: Remove account_id from fabricator

* Update @storybook/addon-actions to version 3.1.8

* Update @storybook/react to version 3.1.8

* Update autoprefixer to version 7.1.2

* Update babel-loader to version 7.1.1

* Update babel-preset-env to version 1.6.0

* Update chai to version 4.1.0

* Update js-yaml to version 3.9.0

* Update jsdom to version 11.1.0

* Update postcss-smart-import to version 0.7.5

* Update sinon to version 2.3.7

* Update substring-trie to version 1.0.1

* Update webpack to version 3.2.0

* Update webpack-manifest-plugin to version 1.1.2

* yarn upgrade

* Upgrade extract-text-webpack-plugin to version 3.0.0

* Upgrade intl-relativeformat to version 2.0.0

* feat: Replace react-swipeable with react-swipeable-views

* fix: iOS 9

* Update chai-enzyme to v0.8.0

* Upgrade precss to v2.0.0

* Upgrade uws to v8.14.0

* Update @storybook/addon-actions to v3.1.6

* Update @storybook/react to v3.1.6

* Update babel-loader to v7.1.0

* Update babel-plugin-transform-react-remove-prop-types to v0.4.6

* Update enzyme to v2.9.1

* Update fsevents to v1.1.2

* Update intersection-observer to v0.3.2

* Update npmlog to v4.1.2

* Update pg to v6.4.0

* Update postcss-loader to v2.0.6

* Update rails-ujs to v5.1.2

* Update react to v15.6.1

* Update react-addons-shallow-compare to v15.6.0

* Update react-dom to v15.6.0

* Update react-notification to v6.7.1

* Update react-test-renderer to v15.6.1

* Update react-textarea-autosize to v5.0.7

* Update redux to v3.7.1

* Update resolve-url-loader to v2.1.0

* Update sass-loader to v6.0.6

* Update sinon to v2.3.5

* Update stringz to v0.2.2

* Update uuid to v3.1.0

* Update websocket.js to v0.1.12

* Update yargs to v8.0.2

* yarn upgrade

Setting ASSET_HOST to `http://0.0.0.0:8080` makes urls in manifest.json to
be invalid, e.g. `http://0.0.0.0:8080/packs/application.js`.

Anyway, we don't need set this on build:development because assets would
be delivered from same origin in development (and w/o dev-server).

ref https://tc39.github.io/proposal-decorators/