Replace sprockets/browserify with Webpack (#2617)

* 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

config/webpack/translationRunner.js

@@ -0,0 +1,34 @@
+const manageTranslations = require('react-intl-translations-manager').default;
+
+manageTranslations({
+  messagesDirectory: 'build/messages',
+  translationsDirectory: 'app/javascript/mastodon/locales/',
+  detectDuplicateIds: false,
+  singleMessagesFile: true,
+  languages: [
+    'ar',
+    'en',
+    'de',
+    'es',
+    'fa',
+    'hr',
+    'hu',
+    'io',
+    'it',
+    'fr',
+    'nl',
+    'no',
+    'oc',
+    'pt',
+    'pt-BR',
+    'uk',
+    'fi',
+    'eo',
+    'ru',
+    'ja',
+    'zh-HK',
+    'zh-CN',
+    'bg',
+    'id',
+  ],
+})