[Attachment] Move Controller and Entities to a Component

There's no problem in having the templates in the core

plugins/Embed/Embed.php

@@ -47,7 +47,7 @@ use App\Core\Log;
 use App\Core\Modules\Plugin;
 use App\Core\Router\RouteLoader;
 use App\Core\Router\Router;
-use App\Entity\Attachment;
+use Component\Attachment\Entity\Attachment;
 use App\Entity\Link;
 use App\Entity\Note;
 use App\Util\Common;