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/admin/src/components/header-secondary.js

@@ -12,7 +12,7 @@ export default class HeaderSecondary extends Component {
   items() {
     var items = new ItemList();
 
-    items.add('user', UserDropdown.component({ user: app.session.user() }));
+    items.add('user', UserDropdown.component({ user: app.session.user }));
 
     return items;
   }