Add sub-directory support

[pjreiniger]

I asked pathplanner to add this last year and it was super helpful for our organization of paths and would love to see it in Choreo as well.

A good first step would be to simply allow / in the path names rather than a massive UI update. Obviously the library would have to recurse the deploy/choreo directory and users would have to call out the parent directory when they call loadTrajectory. Since the GUI seems to sort things alphabetically it would look like a flattened directory tree, but like paths would still be placed next to like paths.