Added setSwipeable() method to Card and CardStack

Added mSwipeable attribute to Card and CardStack. (issue #5)

CardStacks getView method now has some simple logic to determine whether to attach the onTouch listeners. 

We first check the Card with the highest priority. If swipeable is true, than it is swipeable. If false, it is not swipeable. If mSwipeable hasn't been set yet for the Card, we check the CardStack. The same logic applies to the CardStack and the last check is with the Adapter itself (which already has swipeable implemented).

The Example project was also updated to demonstrate a few example cases.