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/features/ui/containers/notifications_container.js

@@ -0,0 +1,21 @@
+import { connect } from 'react-redux';
+import { NotificationStack } from 'react-notification';
+import {
+  dismissAlert,
+  clearAlerts
+} from '../../../actions/alerts';
+import { getAlerts } from '../../../selectors';
+
+const mapStateToProps = (state, props) => ({
+  notifications: getAlerts(state)
+});
+
+const mapDispatchToProps = (dispatch) => {
+  return {
+    onDismiss: alert => {
+      dispatch(dismissAlert(alert));
+    }
+  };
+};
+
+export default connect(mapStateToProps, mapDispatchToProps)(NotificationStack);