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/LoadingPost.js

@@ -0,0 +1,25 @@
+import Component from 'flarum/Component';
+import avatar from 'flarum/helpers/avatar';
+
+/**
+ * The `LoadingPost` component shows a placeholder that looks like a post,
+ * indicating that the post is loading.
+ */
+export default class LoadingPost extends Component {
+  view() {
+    return (
+      <div className="post comment-post loading-post">
+        <header className="post-header">
+          {avatar()}
+          <div className="fake-text"/>
+        </header>
+
+        <div className="post-body">
+          <div className="fake-text"/>
+          <div className="fake-text"/>
+          <div className="fake-text"/>
+        </div>
+      </div>
+    );
+  }
+}