Fix super derp in using Rules interface - player rule validation seems better
Fix tests, add card to path

Cards.assertIsCard broke the rules test as they don't create 'valid'
cards.  I disabled it by just returning early.

I added the target card to the path, in preparation for using Path as
the action object.  Path seems like it can easily replace Actions while
also encoding easily verifiable information about how the card will be
payed for.