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/HeaderSecondary.js

@@ -0,0 +1,57 @@
+import Component from 'flarum/Component';
+import Button from 'flarum/components/Button';
+import LogInModal from 'flarum/components/LogInModal';
+import SignUpModal from 'flarum/components/SignUpModal';
+import SessionDropdown from 'flarum/components/SessionDropdown';
+import NotificationsDropdown from 'flarum/components/NotificationsDropdown';
+import ItemList from 'flarum/utils/ItemList';
+import listItems from 'flarum/helpers/listItems';
+
+/**
+ * The `HeaderSecondary` component displays secondary footer controls, such as
+ * the search box and the user menu. On the default skin, these are shown on the
+ * right side of the header.
+ */
+export default class HeaderSecondary extends Component {
+  view() {
+    return (
+      <ul className="header-controls">
+        {listItems(this.items().toArray())}
+      </ul>
+    );
+  }
+
+  /**
+   * Build an item list for the controls.
+   *
+   * @return {ItemList}
+   */
+  items() {
+    const items = new ItemList();
+
+    items.add('search', app.search.render());
+
+    if (app.session.user) {
+      items.add('notifications', NotificationsDropdown.component());
+      items.add('session', SessionDropdown.component());
+    } else {
+      items.add('signUp',
+        Button.component({
+          children: 'Sign Up',
+          className: 'btn btn-link',
+          onclick: () => app.modal.show(new SignUpModal())
+        })
+      );
+
+      items.add('logIn',
+        Button.component({
+          children: 'Log In',
+          className: 'btn btn-link',
+          onclick: () => app.modal.show(new LogInModal())
+        })
+      );
+    }
+
+    return items;
+  }
+}