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/components/upload_area.js

@@ -0,0 +1,60 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+import { Motion, spring } from 'react-motion';
+import { FormattedMessage } from 'react-intl';
+
+class UploadArea extends React.PureComponent {
+
+  constructor (props, context) {
+    super(props, context);
+
+    this.handleKeyUp = this.handleKeyUp.bind(this);
+  }
+
+  handleKeyUp (e) {
+    e.preventDefault();
+    e.stopPropagation();
+
+    const keyCode = e.keyCode
+    if (this.props.active) {
+      switch(keyCode) {
+      case 27:
+        this.props.onClose();
+        break;
+      }
+    }
+  }
+
+  componentDidMount () {
+    window.addEventListener('keyup', this.handleKeyUp, false);
+  }
+
+  componentWillUnmount () {
+    window.removeEventListener('keyup', this.handleKeyUp);
+  }
+
+  render () {
+    const { active } = this.props;
+
+    return (
+      <Motion defaultStyle={{ backgroundOpacity: 0, backgroundScale: 0.95 }} style={{ backgroundOpacity: spring(active ? 1 : 0, { stiffness: 150, damping: 15 }), backgroundScale: spring(active ? 1 : 0.95, { stiffness: 200, damping: 3 }) }}>
+        {({ backgroundOpacity, backgroundScale }) =>
+          <div className='upload-area' style={{ visibility: active ? 'visible' : 'hidden', opacity: backgroundOpacity }}>
+            <div className='upload-area__drop'>
+              <div className='upload-area__background' style={{ transform: `translateZ(0) scale(${backgroundScale})` }} />
+              <div className='upload-area__content'><FormattedMessage id='upload_area.title' defaultMessage='Drag & drop to upload' /></div>
+            </div>
+          </div>
+        }
+      </Motion>
+    );
+  }
+
+}
+
+UploadArea.propTypes = {
+  active: PropTypes.bool,
+  onClose: PropTypes.func
+};
+
+export default UploadArea;