URL Handling: Removed referrer-based redirect handling

Swapped back handling to instead be pre-determined instead of being
based upon session/referrer which would cause inconsistent results when
referrer data was not available (redirect to app-loaded images/files).

To support, this adds a mechansism to provide a URL through request
data.

Also cleaned up some imports in code while making changes.
Closes #4656.

app/Activity/Controllers/WatchController.php

@@ -24,6 +24,6 @@ class WatchController extends Controller
 
         $this->showSuccessNotification(trans('activities.watch_update_level_notification'));
 
-        return redirect()->back();
+        return redirect($watchable->getUrl());
     }
 }