Operations: add git hooks that will delete empty directories when changing branch

Tools in the python ecosystem often leave cache directories (`__pycache__`). These occupy otherwise empty directories when changing branches and get in the way of having a clean workspace. It may be possible to add git hooks to automatically clean up these empty directories.

See this [stackoverflow post](https://stackoverflow.com/questions/1504724/automatically-remove-pyc-files-and-otherwise-empty-directories-when-i-check-ou

and [this gist](https://gist.github.com/hynekcer/476a593a3fc584278b87#file-post-checkout-py)