Warn if file changed on disk

If the ink script changes on disk, it would be ideal for Inky to recognize this and handle it.

This can be a problem if you are editing in another program (perhaps doing some find/replace-in-all-files or other advance text changes via an external tool), or more commonly, when multiple people on a team edit the same Ink file. Without a warning, it's easy to save over the ink file and lose the other user's changes.

Maybe Inky could display a prompt "Warning: File X has changed on disk. Reload? "?