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/DiscussionRenamedPost.js

@@ -0,0 +1,23 @@
+import EventPost from 'flarum/components/EventPost';
+
+/**
+ * The `DiscussionRenamedPost` component displays a discussion event post
+ * indicating that the discussion has been renamed.
+ *
+ * ### Props
+ *
+ * - All of the props for EventPost
+ */
+export default class DiscussionRenamedPost extends EventPost {
+  icon() {
+    return 'pencil';
+  }
+
+  description() {
+    const post = this.props.post;
+    const oldTitle = post.content()[0];
+    const newTitle = post.content()[1];
+
+    return ['changed the title from ', m('strong.old-title', oldTitle), ' to ', m('strong.new-title', newTitle), '.'];
+  }
+}