Implemented Apple II hi-res bitmap conversion. Supports B&W and
color. Uses essentially the same algorithm as CiderPress.
Experimented with displaying non-text items in ListView. I assumed
it would work, since it's the sort of thing WPF is designed to do,
but it's always wise to approach with caution. Visualization Sets
now show a 64x64 button as a placeholder for the eventual thumbnail.
Some things were being flaky, which turned out to be because I
wasn't Prepare()ing the plugins before using them from Edit
Visualization. To make this a deterministic failure I added an
Unprepare() call that tells the plugin that we're all done.
NOTE: this breaks all existing plugins.
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