Interactively color features #750
Description
There are a couple use cases I've heard for interactively coloring features (and I'm sure there are more):
- Coloring a transcript of interest so you can click around to other transcripts, tracks, etc. and be able to easily go back to the one you were working on. This could be especially important for genes with a lot of transcripts.
- Coloring features different colors to indicate some sort of status, e.g. one color for "done", another color for "in progress", another color for "come back to later".
There's also the idea of programmatically coloring features by e.g. some attribute (which we have in a basic form with gene/pseudogene coloring), and we may want to implement interactive coloring as a special case/shortcut for that.