Add missing ACLs for deleted calendar objects to fix deletion

Due to a bug in Sabre it's necessary for calendar objects to implement
ACLs. Otherwise the scheduling plugin will throw an error when it tries
to fetch the owner of a calendar object that is being deleted.

Ref https://github.com/sabre-io/dav/issues/1345



Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>