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/upload_progress.js

@@ -0,0 +1,43 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+import { Motion, spring } from 'react-motion';
+import { FormattedMessage } from 'react-intl';
+
+class UploadProgress extends React.PureComponent {
+
+  render () {
+    const { active, progress } = this.props;
+
+    if (!active) {
+      return null;
+    }
+
+    return (
+      <div className='upload-progress'>
+        <div className='upload-progress__icon'>
+          <i className='fa fa-upload' />
+        </div>
+
+        <div className='upload-progress__message'>
+          <FormattedMessage id='upload_progress.label' defaultMessage='Uploading...' />
+
+          <div className='upload-progress__backdrop'>
+            <Motion defaultStyle={{ width: 0 }} style={{ width: spring(progress) }}>
+              {({ width }) =>
+                <div className='upload-progress__tracker' style={{ width: `${width}%` }} />
+              }
+            </Motion>
+          </div>
+        </div>
+      </div>
+    );
+  }
+
+}
+
+UploadProgress.propTypes = {
+  active: PropTypes.bool,
+  progress: PropTypes.number
+};
+
+export default UploadProgress;