Card now has properties matched and chosen.
CardMatchingGame now allows to choose a card. If two unmatched cards are chosen, we will try to match them. If it's a match the score will be added to player's score and both cards are marked as matched. If it's not a match the other card will be 'unchosen'.
int -> NSInteger for consistency
Using CardMatchingGame in MatchismoViewController
Removed unused flipsLabel, deck and numberOfClicks properties