Design+API+cardegories (types)

cardegories are classes in ruby under the card namespace, ie.  Card::Number, Card::Person.  Cardegories have a standard class
hierarchy, and are all stored in the cards table via the rails STI mechanism.  'Virtual' cardegories can be created by users through
the interface, and ruby classes are generated on the fly.  The cardegory table for a wagn is the authoritative list of available cardegories for that wagn--
even if a ruby class exists in the code, it must have an entry in the cardegory table to be available for use.

question: do we want to change the 'type' field to 'cardegory' and tell rails to use that as the STI field?