Aggregate multiple group permissions

Change-Id: Ibe8490a175bdf3e9b33c9f690a389fa7348bc972
Remove non-working unique constrant.

uniq contraint won't work properly because id deleted_at by default
is NONE => in mysql NONE != NONE => you are able to create a lot of
records with same volume_id, type, user_or_group_id, deleted

Change-Id: I4e6edf872296b1ed53a27e43dc1d2d0e40659833