I'm not sure how/why this ever happens, but it does, switching the tool when it
shouldn't, which is annoying. I'm also not sure if this fallback is necessary
for some reason, but it seems to work fine without for me.
combines selection related editor properties with the current editor selection.
The related editor properties are:
mouse mode,
zoom setting,
left frame of the canvas,
y origin of the canvas.
Selection state now includes region views (storing the underlying region id)
and time.
This patch also fixes a region mute undo bug.
