Rename ldap_ to institutional_group_

Squashed commit of the following:

commit 07ac25998b53fc60ed2bccc8a982edd56782f2d9
Author: Thomas Schank <DrTom@schank.ch>
Date:   Mon Oct 6 10:15:48 2014 +0200

    Rename ldap_x to institutional_group_x in code

commit 4e3c3d681e93d967f2b1e4180a8ba639c479f059
Author: Thomas Schank <DrTom@schank.ch>
Date:   Mon Oct 6 09:59:54 2014 +0200

    Rename ldap_x to institutional_x in groups table
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