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/compose/components/character_counter.js

@@ -0,0 +1,27 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+import { length } from 'stringz';
+
+class CharacterCounter extends React.PureComponent {
+
+  checkRemainingText (diff) {
+    if (diff < 0) {
+      return <span className='character-counter character-counter--over'>{diff}</span>;
+    }
+    return <span className='character-counter'>{diff}</span>;
+  }
+
+  render () {
+    const diff = this.props.max - length(this.props.text);
+
+    return this.checkRemainingText(diff);
+  }
+
+}
+
+CharacterCounter.propTypes = {
+  text: PropTypes.string.isRequired,
+  max: PropTypes.number.isRequired
+}
+
+export default CharacterCounter;