WIP: Region selection on ARPanel.
Draw a box on an ARDisplay.
Removing selection from display.  Headed towards a layered approach.
Renamed 'compound' to a more descritive name.
WIP: Infrastructure changes for enhance button (doesn't work yet).
Rebuild zoom/pan machinery into simpler system.  Closes #29
Subset render under new architecture working (and misc other fixes).
Overlay infrastructure draft complete.  Time to tie-in subset-based specialization.
Improved mask/unmask overlay information.
More work on overlay
Overlay selection region tracks dataspace.
Enhance button works...but you have to toggle it for every change.
Enhance stable under zoom/pan (at the cost of the view-relative transfer flag).
Enhance button stability under zoom...but there is flicker.
Multi-rectangular enhance working (still flickers).
Removed zoom-flicker (and added bounding-box showing focus region when enhance is enabled). Closes #13 (but I'm sure I'll tweak the visuals a bit more).