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/stream.js

@@ -0,0 +1,22 @@
+import WebSocketClient from 'websocket.js';
+
+const createWebSocketURL = (url) => {
+  const a = document.createElement('a');
+
+  a.href     = url;
+  a.href     = a.href;
+  a.protocol = a.protocol.replace('http', 'ws');
+
+  return a.href;
+};
+
+export default function getStream(streamingAPIBaseURL, accessToken, stream, { connected, received, disconnected, reconnected }) {
+  const ws = new WebSocketClient(`${createWebSocketURL(streamingAPIBaseURL)}/api/v1/streaming/?access_token=${accessToken}&stream=${stream}`);
+
+  ws.onopen      = connected;
+  ws.onmessage   = e => received(JSON.parse(e.data));
+  ws.onclose     = disconnected;
+  ws.onreconnect = reconnected;
+
+  return ws;
+};