Ongoing refactoring.

1. Delete AnimationController and AnimationControllerSpec.
2. Move required AnimationController functionality to AnimationViewModel.
3. Add a new ClockViewModel to eventually be shared across widgets.
4. Add AnimationViewModelSpec (though tests are a mess).
5. Revert many of the changes to Clock/ClockRange/ClockStep to be closer inline with master.

Still a ton of cleanup to be done.