File list improvements

[zachrammell]

This adds some minor quality-of-life operations related to staging changes, like double-clicking to stage/unstage, and treating unstaging a rename as unstaging both the move and delete.

I also added a new path display style inspired by other software, which shows the filename first with the path after. The rendering logic changes for this are perhaps a little messy and the part I'd seek the most feedback on.

[jorio]

This is great! Do you mind splitting these features into separate PRs so they're easier to merge individually?

Some thoughts:

• Unstage 'R' in one go: Cool! Thanks for the test, I think this is good to go.
• Detect renames in unstaged changes: Rename detection can be expensive, so I'd like to do some benchmarking to see how this affects large workdirs before we make this the default. But I see how people can find this useful, so perhaps this could be an option that isn't enabled by default, for now? We should also add a test to enshrine this behavior.
• Filename first: Looking great! I realize that testing text rendering can be tricky, but we can still add a simple test for coverage of the new code paths - just to make sure future refactors don't break this. (You can run test.py --cov and you'll get a coverage report that looks like this.)
• D-Click to stage: I actually had a prototype for this that didn't make it into v1.6. My implementation overloads the "middle click to stage" setting that already exists. I cleaned it up and pushed it as a WIP branch if you want to see my approach.

I'll take a closer look at your rendering implementation when I have some time this week. Thank you for your contribution!