Various cleanup

In the Walkthrough (hw0) we had to have a Matchismo game that can
handle multiple cards and implement the 2-card game in a model class.
Also it had a flips and a score Label. It's basically what Paul showed
us in Lecture 1, 2 and 3.
In hw1 we then had to add 4 cards, a Deal Button and a textual
outcomeLabel of the result. A UIsegmentedControl was used to switch
between 2-card- and 3-card-matching mode. A UIImage should be used as
the back of the card. Still Lecture 1, 2 and 3. Important: MVC!
hw2 introduced a tab bar controller to a Set Game, hw1 had to be intact
expect we are allowed to remove the UISegmentedControl.
NSAttributedStrings hat to be used for the different card faces.
Lecture 4&5. Important OOP!
Any Extra Credits for hw1 and hw2 are supposed to happen on this branch