Admin interface: improve workflow of managing meta key definitions

Squashed commit of the following:

commit b3c28c3563dbd7766987d29dff49bdb85ca11ebb
Author: Michał Podlecki <m.podlecki@op.pl>
Date:   Tue Aug 26 09:48:45 2014 +0200

    Admin interface: improve workflow of managing meta key definitions