Bitmap animations are composed of a sequence of other visualizations.
This is all well and good until a visualization is deleted, at which
point all animations in all sets in the entire project have to be
checked and potentially changed, and perhaps even removed (if all of
the animation's members have been removed). This turns out to be
kind of annoying to deal with, but it's better to deal with it in
code than force the user to manually update broken animations.
This change adds thumbnails for the animations, currently generated
by offscreen composition. This approach doesn't work quite right.
This adds a new class and a rough GUI for the editor. Animated
visualizations take a collection of bitmaps and display them in
sequence. (This will eventually become an animated GIF.)
Fixed the issue where changes to tags in the set currently being
edited weren't visible to the tag uniqueness check when editing other
items in the same set.
