Refactored some core entity actions

- Created BookChild class to share some page/chapter logic.
- Gave entities the power to generate their own permissions and slugs.
- Moved bits out of BaseController constructor since it was overly
sticky.
- Moved slug generation logic into its own class.
- Created a facade for permissions due to high use.
- Fixed failing test issues from last commits

app/Actions/ActivityService.php

@@ -73,6 +73,7 @@ class ActivityService
      */
     public function removeEntity(Entity $entity)
     {
+        // TODO - Rewrite to db query.
         $activities = $entity->activity;
         foreach ($activities as $activity) {
             $activity->extra = $entity->name;