get wave drawing improved, but commit before i tear it all up and go back to a single cached image per waveview
new image cache design for waveviews, with various fixes.

Rather than maintain a set of images in a cache, when we no longer have the required waveform data, create a new image that is appropriately centered and extends to roughly twice the screen width (or the limits of the region's source file(s), as necessary)
set waveform color to a V-reduced version of the frame fill color.
(working) start of an experiment with pyramix-style waveform drawing