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/avatar.js

@@ -0,0 +1,68 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+
+class Avatar extends React.PureComponent {
+
+  constructor (props, context) {
+    super(props, context);
+
+    this.state = {
+      hovering: false
+    };
+
+    this.handleMouseEnter = this.handleMouseEnter.bind(this);
+    this.handleMouseLeave = this.handleMouseLeave.bind(this);
+  }
+
+  handleMouseEnter () {
+    if (this.props.animate) return;
+    this.setState({ hovering: true });
+  }
+
+  handleMouseLeave () {
+    if (this.props.animate) return;
+    this.setState({ hovering: false });
+  }
+
+  render () {
+    const { src, size, staticSrc, animate } = this.props;
+    const { hovering } = this.state;
+
+    const style = {
+      ...this.props.style,
+      width: `${size}px`,
+      height: `${size}px`,
+      backgroundSize: `${size}px ${size}px`
+    };
+
+    if (hovering || animate) {
+      style.backgroundImage = `url(${src})`;
+    } else {
+      style.backgroundImage = `url(${staticSrc})`;
+    }
+
+    return (
+      <div
+        className='account__avatar'
+        onMouseEnter={this.handleMouseEnter}
+        onMouseLeave={this.handleMouseLeave}
+        style={style}
+      />
+    );
+  }
+
+}
+
+Avatar.propTypes = {
+  src: PropTypes.string.isRequired,
+  staticSrc: PropTypes.string,
+  size: PropTypes.number.isRequired,
+  style: PropTypes.object,
+  animate: PropTypes.bool
+};
+
+Avatar.defaultProps = {
+  animate: false
+};
+
+export default Avatar;