Massive JavaScript cleanup

- Use JSX for templates
- Docblock/comment everything
- Mostly passes ESLint (still some work to do)
- Lots of renaming, refactoring, etc.

CSS hasn't been updated yet.

js/forum/src/components/EventPost.js

@@ -0,0 +1,51 @@
+import Post from 'flarum/components/Post';
+import usernameHelper from 'flarum/helpers/username';
+import icon from 'flarum/helpers/icon';
+
+/**
+ * The `EventPost` component displays a post which indicating a discussion
+ * event, like a discussion being renamed or stickied. Subclasses must implement
+ * the `icon` and `description` methods.
+ *
+ * ### Props
+ *
+ * - All of the props for `Post`
+ *
+ * @abstract
+ */
+export default class EventPost extends Post {
+  attrs() {
+    return {
+      className: 'event-post ' + this.props.post.contentType() + '-post'
+    };
+  }
+
+  content() {
+    const user = this.props.post.user();
+    const username = usernameHelper(user);
+
+    return [
+      icon(this.icon(), {className: 'event-post-icon'}),
+      <div class="event-post-info">
+        {user ? <a className="post-user" href={app.route.user(user)} config={m.route}>{username}</a> : username}
+        {this.description()}
+      </div>
+    ];
+  }
+
+  /**
+   * Get the name of the event icon.
+   *
+   * @return {String}
+   */
+  icon() {
+  }
+
+  /**
+   * Get the description of the event.
+   *
+   * @return {VirtualElement}
+   */
+  description() {
+  }
+}