Added assignment 2. Reviewed and rewritten model code.

Renamed controller. Added attributedDescription instance method to Card
model. Refactored code, simplify logic. Used NSCountedSet for set game
rules. Init methods now operates with instance variables, not
properties. Added introspection. Changed way of invoking class methods
in itself ([[self class] classMethod]). Added set card model and set
deck model with 81 cards. Added blue background for set game. Added
controller for set game.