WIP: New transition styles

I wanted to revisit our transitions and clean them up a bit. When we went to the box-shadow style iOS 7 transitions, we hit some performance issues. I tried a different approach that I think is better and lighter weight, and gets a similar effect.

Also, I've gone through and cleaned up references to `ios7` and normalized them to just `ios`. I did it in a simple way such that all the previous code should still work and it's backwards compatible.

Also, I added a new transition called `slide-full` that does a full slide rather than the offset slide on iOS, that I think is a better fit for Android.