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/DiscussionRenamedNotification.js

@@ -0,0 +1,26 @@
+import Notification from 'flarum/components/Notification';
+import username from 'flarum/helpers/username';
+
+/**
+ * The `DiscussionRenamedNotification` component displays a notification which
+ * indicates that a discussion has had its title changed.
+ *
+ * ### Props
+ *
+ * - All of the props for Notification
+ */
+export default class DiscussionRenamedNotification extends Notification {
+  icon() {
+    return 'pencil';
+  }
+
+  href() {
+    const notification = this.props.notification;
+
+    return app.route.discussion(notification.subject(), notification.content().postNumber);
+  }
+
+  content() {
+    return [username(this.props.notification.sender()), ' changed the title'];
+  }
+}