fixes #2455 hostgroup not saving
fixes #2393 - Couple of models broken with audited 3.0.0

this is not a fix for the mass assignment problem, rather just to solve immedient packaing issue upstream.

a follow up on mass assignment should be done via another commit.
fixes #2132 Smart Variables in hostgroup.
1. Show smart variables in hostgroup view.
2. Added the GUI to override smart variables values in host group.