Add SpinnerView. Works on Chrome (and mobile), "works" on IE, not on FF

IE it spins put doesn't stretch and shrink. Doesn't animate smoothly, but jumpy.
It's a spinner within the meaning of the thing, though.

Firefox shows something moving, but it renders oddly and is only visible in a
flickering sort of way.

Includes a demo, demos/spinner.html
Add FutureView and demo

This view shows a spinner (defaults to SpinnerView) until the provided future
resolves.