* renamed the 'frame' AssetSet to 'frames'
 * removed @Immutable from the descriptor stuff
 * added setting keys down the descriptor tree so items don't have to know about their parents
 * made the internal descriptor stuff @PackageScope
 * add getImageAsset on AssetSet for getting an ImageAsset from a set
 * tweaked the artwork box in the screen descriptor
added creature frames.  One could argue that overlaying the power/toughness box on the normal frame is better, but I'm not convinced.
assembled a card descriptor and compositor framework for describing the two halves of a given card, along with a super-primitive and not-yet-complete AWT-based compositor to create cards from a model.