Spinny updates

* Add separate bg and mask paths to spinny -- the cover art goes between them
* Use pixmaps instead of images for scalable drawing
* Update LateNight with SVG spinnies

This doesn't work right -- the spinnies are drawing aliased even though the hint says antialiased.  I copied the drawing code from wknobcomposed so I'm not sure why it looks bad
Since WKnobComposed was added in 1.12 I didn't add that since there are no skins that use it. For consistency we could do that though.