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/admin/components/DashboardWidget.js

@@ -0,0 +1,38 @@
+/*
+ * This file is part of Flarum.
+ *
+ * (c) Toby Zerner <toby.zerner@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+import Component from '../../common/Component';
+
+export default class Widget extends Component {
+  view() {
+    return (
+      <div className={"Widget "+this.className()}>
+        {this.content()}
+      </div>
+    );
+  }
+
+  /**
+   * Get the class name to apply to the widget.
+   *
+   * @return {String}
+   */
+  className() {
+    return '';
+  }
+
+  /**
+   * Get the content of the widget.
+   *
+   * @return {VirtualElement}
+   */
+  content() {
+    return [];
+  }
+}