Fixes #5188

* Upgrade to React 16.0.0

* Disable some uncritical tests while chai-enzyme remains incompatible

A new rake task emojis:generate downloads a full list of valid
unicode sequences from unicode.org and checks it against existing
Twemoji files, finally generating a map from each sequence to the
existing file (e.g. when there's multiple ways an emoji can be
expressed). The map is dumped into app/javascript/mastodon/emoji_map.json

That file is loaded by emojione_light.js (now a misnomer) which
decorates it further with shortcodes taken from emoji-mart's index.

* 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

* feat: Cache status height to avoid expensive renders

* feat: Escape content and emojify in reducers

* fix(css): Remove backface-visibility: hidden from .scrollable

* fix(statuses): Avoid creating DOMParses inside a loop

* Refactored Avatar and AvatarOverlay (DRY) to have 'account' as prop.
Also removed animate attribute from compose navigation bar, which should
have never been there. Added test for avatar overlay.

* fix broken tests

* god dammit another bug in tests! travis please let this pass

* formatting in avatar overlay

* fix(dropdown_menu): Open as modal on mobile

* fix(dropdown_menu): Open modal on touch

* fix(dropdown_menu): Show status

* fix(dropdown_menu): Max dimensions and reduce padding

* chore(dropdown_menu): Test new functionality

* refactor: Use DropdownMenuContainer instead of DropdownMenu

* feat(privacy_dropdown): Open as modal on touch devices

* feat(modal_root): Do not load actions-modal async

* 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

- Use unicode when selecting emoji through picker
- Convert shortcodes to unicode when storing text input server-side
- Do not convert shortcodes in JS anymore

* Faster emojify() algorithm, avoid regex replace

* add semicolon

* Add quotes ESLint rule

* Add jsx-quotes ESlint rule

* Sort ESLint rules

- Upgrade dependencies
    - chai (3.5.0 -> 4.0.1)
    - chai-enzyme (0.6.1 -> 0.7.1)
    - sinon (2.2.0 -> 2.3.2)
- Change extensions from .jsx to .js
- Don't assign `React` to `global`
- Check code format using ESLint

* refactor(components/status_list): Avoid quering scrollTop if not necessary

* refactor(components/dropdown_menu): Do not render items if not expanded

* refactor: Cherry-pick react-motion imports

* refactor(compose/privacy_dropdown): Do not render options if not open

* refactor(components/column_collapsable): Do not render children if collapsed

* Replace browserify with webpack

* Add react-intl-translations-manager

* Do not minify in development, add offline-plugin for ServiceWorker background cache updates

* Adjust tests and dependencies

* Fix production deployments

* Fix tests

* More optimizations

* Improve travis cache for npm stuff

* Re-run travis

* Add back support for custom.scss as before

* Remove offline-plugin and babili

* Fix issue with Immutable.List().unshift(...values) not working as expected

* Make travis load schema instead of running all migrations in sequence

* Fix missing React import in WarningContainer. Optimize rendering performance by using ImmutablePureComponent instead of
React.PureComponent. ImmutablePureComponent uses Immutable.is() to compare props. Replace dynamic callback bindings in
<UI />

* Add react definitions to places that use JSX

* Add Procfile.dev for running rails, webpack and streaming API at the same time

* When avatar/header are GIF, generate static versions.
Account API returns "avatar"/"avatar_static", "header"/"header_static"
Static version is the same as original for other cases
Web UI de-animates avatars in toots, lists of users

Fix #441, fix #596, prerequisite for #1064

* Fix JS test

* Add rake task to generate static avatars/headers from GIF ones, add test