Add ability to restrict card swipe direction.

Added a field to specify a single direction for cards in a CardListView to be able to be swiped. Cards in a CardListView can be swiped left, right or both. The default, if not set, is both (the same behavior as it is currently). 

I needed this feature for a project I am working on. I'm not sure if you're interested in including it, but thought I'd propose it just in case.