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/lib/helpers/username.js

@@ -1,5 +1,12 @@
+/**
+ * The `username` helper displays a user's username in a <span class="username">
+ * tag. If the user doesn't exist, the username will be displayed as [deleted].
+ *
+ * @param {User} user
+ * @return {Object}
+ */
 export default function username(user) {
-  var username = (user && user.username()) || '[deleted]';
+  const name = (user && user.username()) || '[deleted]';
 
-  return m('span.username', username);
+  return <span className="username">{name}</span>;
 }