CardMatchingGame interface and implementation completed.

Added public interface for CardMatchingGame from lecture video.
Completed implementation of all API from lecture video.
Completed lecture 3 code.

Completed coding demoed in lecture 3.
Modified storyboard to have 12 cards in an outlet collection.
Removed flip score label and counter
Added utility methods to set cardButton contents and image
Added score label and counter
Updated PlayingCard match method to work properly for playing cards.

Project is ready for assignment 2now.