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

app/javascript/mastodon/reducers/index.js

@@ -0,0 +1,38 @@
+import { combineReducers } from 'redux-immutable';
+import timelines from './timelines';
+import meta from './meta';
+import compose from './compose';
+import alerts from './alerts';
+import { loadingBarReducer } from 'react-redux-loading-bar';
+import modal from './modal';
+import user_lists from './user_lists';
+import accounts from './accounts';
+import accounts_counters from './accounts_counters';
+import statuses from './statuses';
+import relationships from './relationships';
+import search from './search';
+import notifications from './notifications';
+import settings from './settings';
+import status_lists from './status_lists';
+import cards from './cards';
+import reports from './reports';
+
+export default combineReducers({
+  timelines,
+  meta,
+  compose,
+  alerts,
+  loadingBar: loadingBarReducer,
+  modal,
+  user_lists,
+  status_lists,
+  accounts,
+  accounts_counters,
+  statuses,
+  relationships,
+  search,
+  notifications,
+  settings,
+  cards,
+  reports
+});