uninstall / cleanup script?

Putting everything in `/opt` is a great idea, but as per issue #6, it might be a good idea to add certain files / links to other areas of the system, not least in the places where DMs look for sessions - e.g. in `/usr/share/wayland-sessions/`

If that is implemented, then some kind of cleanup script is also warranted, to remove everything from a system automatically. 