Admin interface: fix setting special sets

Squashed commit of the following:

commit 757601840443052befc6cfd6674b7ed75d7d6049
Author: Michał Podlecki <m.podlecki@op.pl>
Date:   Mon Sep 29 15:34:16 2014 +0200
Work on ldap_cleaning migration ...
Clean zhdk group metadata (LDAP)