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/forum/components/PostPreview.js

@@ -0,0 +1,30 @@
+import Component from '../../common/Component';
+import avatar from '../../common/helpers/avatar';
+import username from '../../common/helpers/username';
+import highlight from '../../common/helpers/highlight';
+
+/**
+ * The `PostPreview` component shows a link to a post containing the avatar and
+ * username of the author, and a short excerpt of the post's content.
+ *
+ * ### Props
+ *
+ * - `post`
+ */
+export default class PostPreview extends Component {
+  view() {
+    const post = this.props.post;
+    const user = post.user();
+    const excerpt = highlight(post.contentPlain(), this.props.highlight, 300);
+
+    return (
+      <a className="PostPreview" href={app.route.post(post)} config={m.route} onclick={this.props.onclick}>
+        <span className="PostPreview-content">
+          {avatar(user)}
+          {username(user)}{' '}
+          <span className="PostPreview-excerpt">{excerpt}</span>
+        </span>
+      </a>
+    );
+  }
+}