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/dropdown_menu.js

@@ -0,0 +1,79 @@
+import React from 'react';
+import Dropdown, { DropdownTrigger, DropdownContent } from 'react-simple-dropdown';
+import PropTypes from 'prop-types';
+
+class DropdownMenu extends React.PureComponent {
+
+  constructor (props, context) {
+    super(props, context);
+    this.state = {
+      direction: 'left'
+    };
+    this.setRef = this.setRef.bind(this);
+    this.renderItem = this.renderItem.bind(this);
+  }
+
+  setRef (c) {
+    this.dropdown = c;
+  }
+
+  handleClick (i, e) {
+    const { action } = this.props.items[i];
+
+    if (typeof action === 'function') {
+      e.preventDefault();
+      action();
+      this.dropdown.hide();
+    }
+  }
+
+  renderItem (item, i) {
+    if (item === null) {
+      return <li key={ 'sep' + i } className='dropdown__sep' />;
+    }
+
+    const { text, action, href = '#' } = item;
+
+    return (
+      <li className='dropdown__content-list-item' key={ text + i }>
+        <a href={href} target='_blank' rel='noopener' onClick={this.handleClick.bind(this, i)} className='dropdown__content-list-link'>
+          {text}
+        </a>
+      </li>
+    );
+  }
+
+  render () {
+    const { icon, items, size, direction, ariaLabel } = this.props;
+    const directionClass = (direction === "left") ? "dropdown__left" : "dropdown__right";
+
+    return (
+      <Dropdown ref={this.setRef}>
+        <DropdownTrigger className='icon-button' style={{ fontSize: `${size}px`, width: `${size}px`, lineHeight: `${size}px` }} aria-label={ariaLabel}>
+          <i className={ `fa fa-fw fa-${icon} dropdown__icon` }  aria-hidden={true} />
+        </DropdownTrigger>
+
+        <DropdownContent className={directionClass}>
+          <ul className='dropdown__content-list'>
+            {items.map(this.renderItem)}
+          </ul>
+        </DropdownContent>
+      </Dropdown>
+    );
+  }
+
+}
+
+DropdownMenu.propTypes = {
+  icon: PropTypes.string.isRequired,
+  items: PropTypes.array.isRequired,
+  size: PropTypes.number.isRequired,
+  direction: PropTypes.string,
+  ariaLabel: PropTypes.string
+};
+
+DropdownMenu.defaultProps = {
+  ariaLabel: "Menu"
+};
+
+export default DropdownMenu;