Update basket only when functional area memberships change.
[fix bug 908053] Fix group member counts in admin.
Add GroupManager that provides member_count.

* Also add total_member_count, full_member_count and
  pending_member_count in Admin Panel.
Beautify GroupAdmin.
[fix bug 980887] Speedup group browsing.
[fix bug 1000938] Proper filtering for group memberships.
Tests cleanup.
Merge pull request #922 from glogiotatidis/groupscleanup

Groups cleanup