make recovery UI images more general; allow for installation animation

Change some of the UI parameters (# of indeterminate progress bar
frames, fps, etc.) from #defined constants to variables that can be
set by the device-specific recovery_ui code (via a new function).

Support overlaying different images on top of the base installation
icon to animate it.  Make the FPS control more accurate.

Change-Id: I9268b389b7ea6b3ed9e0c7eae37baf4272e60edd