Replace graph with UICollectionViewController

Closes #22 

Replaced the single UIView with drawRect for the graph with a UICollectionViewController.  Each bar is now VoiceOver compatible.  The Collection View allows for animation transitions, cell reuse, and is much more reusable.  The animation during rotation needs some tweaking but I think that'll happen in another PR.

This PR does not change the following:
* Stats data structures
* Logic for display of colors, labels, etc
* Remote logic