* Replace the radio buttons for Page Type and Wallpaper with the new
SelectBox widgets from the UI toolkit.
* Choice of default palette also switched from a MenuButton to
a SelectBox widget.
* Experimental "Browse..." option added to the Wallpaper drop-down when
run in --experimental mode; not yet functional.
* In the "New Level" dialog, a "Palette:" option shows a MenuButton
drop-down with options: Default, Colored Pencil, and Blueprint. These
control the set of colors the new level starts with.
* Added Feature Flag support, run doodle with --experimental to enable
all flags. Eraser Tool is behind a feature flag now.
* + and - on the top row of keyboard keys will zoom the drawing in and
out in Edit Mode. The wallpaper zooms nicely enough, but level
chunkers need work.
* A View menu is added with Zoom in/out, reset zoom, and scroll to
origin options. The whole menu is behind the Zoom feature flag.
* Update README with lots of details for fun debug mode options to play
around with.
