As with still images, animations are rendered at original size and
then scaled with HTML properties.
Also, fixed the blurry scaling on animation thumbnails. I couldn't
find a way to do nearest-neighbor scaling in the code-behind without
resorting to System.Drawing (WinForms), so I added an overlay image
to the various grids.
The UI was moving items from the source list to the animation list,
but there's no reason why the same thing can't appear more than once.
You can no longer hit "Add" repeatedly to add multiple consecutive
items, but you can now multi-select in the source list to add several
things at once.
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.
