DON'T MERGE YET: Set minimum supported version of iOS to 6, and fix all deprecation warnings

This PR drops support for iOS 5.1, sets the minimum supported version of iOS to 6.0, and fixes all iOS 6.0 deprecation warnings in the app.

This shouldn't be merged until we finish hammering out this topic: https://groups.google.com/forum/#!topic/onebusaway-developers/2Niw7mU5GEM