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/components/collapsable.js

@@ -0,0 +1,21 @@
+import React from 'react';
+import { Motion, spring } from 'react-motion';
+import PropTypes from 'prop-types';
+
+const Collapsable = ({ fullHeight, isVisible, children }) => (
+  <Motion defaultStyle={{ opacity: !isVisible ? 0 : 100, height: isVisible ? fullHeight : 0 }} style={{ opacity: spring(!isVisible ? 0 : 100), height: spring(!isVisible ? 0 : fullHeight) }}>
+    {({ opacity, height }) =>
+      <div style={{ height: `${height}px`, overflow: 'hidden', opacity: opacity / 100, display: Math.floor(opacity) === 0 ? 'none' : 'block' }}>
+        {children}
+      </div>
+    }
+  </Motion>
+);
+
+Collapsable.propTypes = {
+  fullHeight: PropTypes.number.isRequired,
+  isVisible: PropTypes.bool.isRequired,
+  children: PropTypes.node.isRequired
+};
+
+export default Collapsable;