Query parameters implemented as per the doc

Kept Attachment entity compatible with GS Master
Fixed conversation id data type on Notice entity

classes/Activitypub_attachment.php

@@ -45,7 +45,7 @@ class Activitypub_attachment extends Managed_DataObject
         'id'        => $attachment->getID (),
         'mimetype'  => $attachment->mimetype,
         'url'       => $attachment->getUrl (),
-        'size'      => $attachment->getSize (),
+        'size'      => intval($attachment->size),
         'title'     => $attachment->getTitle (),
         'meta'      => null
       ];