Add requestAnimationFrame mode

[panathea]

It would be nice if <Play /> took a prop that made it start updating in realtime, instead of having to build that code ourselves all the time like in the fade and scrubbing stories.

Maybe something like animate, realtime, redraw, or live as a prop that enables the mode?

Should probably make use of a requestAnimationFrame polyfill. This would, however, introduce a dependency. Better than rolling my own.