Fixes for special groups

Sorry for the whitespace "modifications", those were not intentional. Only changes there are giving a label to user_groups and specifying a selector to filter special groups away from the dropdown.

The other commit makes special groups instance vars so that they're initialized only once (instead of every call to find() or viewable()).

And from now on there will be no commits to the master in this fork by me, but only fetch and merge from upstream. It's easy once you find out the right way...