better handling of Cardtype removal+issues

(Also see Can't remove or change Cardtype of Cardtype cards)

I tried to remove School (a Cardtype) and got "connecting to server..." for ~10 seconds then done but the card was still there. There was one card of that type, so i changed it to Basic, then removed the card.

Should get a warning of some kind i guess, and maybe the option to remove the card anyway (changing all those cards to Basic?).

Anyway, then i recreated School, as a Cardtype card, and it didn't show up as an option in Cardtype menus. So i tried changing it's Cardtype to Basic (thinking to then switch it back to Cardtype to see if that helpd), but just selecting Basic in the Cardtype menu got:

Oh, Man. You uncovered a bug in Wagn.

undefined method `class_name' for nil:NilClass

An email about this error has been sent to the authors of Wagn