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/models/forum.js

@@ -1,5 +1,3 @@
-import Model from 'flarum/model';
+import Model from 'flarum/Model';
 
-class Forum extends Model {}
-
-export default Forum;
+export default class Forum extends Model {}