Rework notifications architecture

- The recipient(s) are the concern of the notifier/sender, not the
notification itself
- Allow “retraction” of notifications (e.g. if a discussion is
stickied, but then it is unstickied)
- Misc. cleanup

src/Core/Repositories/EloquentNotificationRepository.php

@@ -5,15 +5,15 @@ use DB;
 
 class EloquentNotificationRepository implements NotificationRepositoryInterface
 {
-    public function findByUser($userId, $count = null, $start = 0)
+    public function findByUser($userId, $limit = null, $offset = 0)
     {
         $primaries = Notification::select(DB::raw('MAX(id) AS id'), DB::raw('SUM(is_read = 0) AS unread_count'))
             ->where('user_id', $userId)
             ->whereIn('type', array_keys(Notification::getTypes()))
             ->groupBy('type', 'subject_id')
             ->orderBy('time', 'desc')
-            ->skip($start)
-            ->take($count);
+            ->skip($offset)
+            ->take($limit);
 
         return Notification::with('subject')
             ->select('notifications.*', 'p.unread_count')