Webpack (#1367)

* Replace gulp with webpack and npm scripts for JS compilation
* Set up Travis CI to commit compiled JS
* Restructure `js` directory; only one instance of npm, forum/admin are "submodules"
* Refactor JS initializers into Application subclasses
* Maintain partial compatibility API (importing from absolute paths) for extensions
* Remove minification responsibility from PHP asset compiler
* Restructure `less` directory

js/src/common/components/Select.js

@@ -0,0 +1,25 @@
+import Component from '../Component';
+import icon from '../helpers/icon';
+
+/**
+ * The `Select` component displays a <select> input, surrounded with some extra
+ * elements for styling. It accepts the following props:
+ *
+ * - `options` A map of option values to labels.
+ * - `onchange` A callback to run when the selected value is changed.
+ * - `value` The value of the selected option.
+ */
+export default class Select extends Component {
+  view() {
+    const {options, onchange, value} = this.props;
+
+    return (
+      <span className="Select">
+        <select className="Select-input FormControl" onchange={onchange ? m.withAttr('value', onchange.bind(this)) : undefined} value={value}>
+          {Object.keys(options).map(key => <option value={key}>{options[key]}</option>)}
+        </select>
+        {icon('fas fa-sort', {className: 'Select-caret'})}
+      </span>
+    );
+  }
+}