Initial refactor of client actions, data preloading, SEO

An initial stab at flarum/core#126. Still WIP. Preliminary
implementation of flarum/core#128 and flarum/core#13.

js/lib/models/forum.js

@@ -0,0 +1,5 @@
+import Model from 'flarum/model';
+
+class Forum extends Model {}
+
+export default Forum;