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/UsersSearchSource.js

@@ -0,0 +1,36 @@
+import highlight from 'flarum/helpers/highlight';
+import avatar from 'flarum/helpers/avatar';
+
+/**
+ * The `UsersSearchSource` finds and displays user search results in the search
+ * dropdown.
+ *
+ * @implements SearchSource
+ */
+export default class UsersSearchResults {
+  search(query) {
+    return app.store.find('users', {
+      filter: {q: query},
+      page: {limit: 5}
+    });
+  }
+
+  view(query) {
+    const results = app.store.all('users')
+      .filter(user => user.username().toLowerCase().substr(0, query.length) === query);
+
+    if (!results.length) return '';
+
+    return [
+      <li className="dropdown-header">Users</li>,
+      results.map(user => (
+        <li className="user-search-result" data-index={'users' + user.id()}>
+          <a href={app.route.user(user)} config={m.route}>
+            {avatar(user)}
+            {highlight(user.username(), query)}
+          </a>
+        </li>
+      ))
+    ];
+  }
+}