New usergroup discussions

Hi guys. We, edev and Swap, have managed to give the noding collective new usergroup discussions. Previously, only eds and admins had these, but we reckon there is no reason why anybody can't have one of these.

Swap wrote the code which was already kinda half-written by kthejoker in order to transition from discussion pages for only the staff, to discussion pages for every usergroup, while edev helped with a brief but intense debugging session. Kudos in particular to DonJaime, OldMiner, BlackPawn, raincomplex, and Oolong for helping with the alpha testing. Hope you noders like our work.

All the desired functionality is there, but there are still some minor cosmetic changes that may happen soon. As is usual, although we did spend some time debugging this, the odd bug might have managed to scurry past our nets anyways. As such, I'm calling this beta, with changes to happen soon. Bugs go to Swap and edev.