Note: the `__update_widget()` method, while it doesn't have any visible delay
has the potential for improvement. I didn't do it because it felt like
premature optimization.
MoveGamePopUp: update it to use RareGame and it's signals
RareGame: Add `install_path` attribute and change `needs_verification` setter
Now both setters will update the local `igame` attribute and save it too.
MoveWorker: Update it to use RareGame.
Other changes include moving "same-drive" moving into the worker and using
`os.path` methods instead of `PathLib`
SteamGrades: Remove worker, it is implemented in RareGame now.
