Add ripple and remove weird piece-meal animation where items came in after the card

Also, update to minsdk 21 to use <ripple>.

Still to-do: figure out how to make the bottom sheet come up under the navigation bar instead of on top of it.
The best I can say is that the animation happens on the "RenderThread" that was hyped during I/O. It isn't being explicitly started anywhere, and the RippleDrawable class has no way to attach a listener for when the animation is complete.