#5 (auto)save thumbnails

[adonais]

How about a "Save Thumbnail" button under the Preview pane in the
Flame window, that takes the already rendered 128x96 preview and saves
it down to PNG? Clicking the button could either open a save dialogue to
enter the file name, or it just saves to a default file name without
prompting the user (option to be set in Preferences?).

Just in order to facilitate quick graphical browsing of genomes through
the Finder, without needing to load each one into Oxidizer first just to
check what it looks like.