Added Assignment 2 including several extra credit items

Key points:
- Figured out how to rename a project (from Matchismo to Set)
- Tried to focus on (e.g. learn!) subclassing but also not subclassing
all CardGame classes, ony those that I thought were needed. Created
PlayingCard and Set subclasses: View Controller, Card, and Deck.
- Professors's example using kindOfClass very helpful!
- Rather than override the UIUpdate method, I broke this method into
several smaller methods. In retrospect, maybe a bit more work that was
needed.
- Symbols, colors, etc. defined in SetCard. Case could be make that
SetCard should have generic symbols, colors, etc. or even generic
attributes e.g red would be Attribute 1 Value 1, green woudl be
Attribute 1 Value 2, etc. However, then the ViewController would need
to have a lot of logic converting Attributes and Values to the screen.
My view was that these are attributes of a SetCard.

It would be interesting though to only have a very generic Card, not
needing a SetCard or PlayingCard.