group admin panel tweaks

looks like : 
[![](http://i.imgur.com/p5HJCjM.png)](http://i.imgur.com/p5HJCjM.png)

## features

- a couple more scopes, most significantly, the "parent only" scope. some beginnings at being able to see inactive groups
- a collapse of the "group_memberships_count" & "max_size" columns into the "size" column  e.g. ` 27 (50) ` means 27 in group, max_size=50. *NB* if no bracket is present, the group is a subgroup. perhaps there should be a parent group col?
- a button which toggles pagination from a default of 40 to 9999999 (requested by Ben). this feature is to be watched to see if it taxes the system too much.