Option: mouse_integration

AKA magic mouse / mousehack / virtual mouse driver

This option implies (unless overriden):
- cursor = 0
- automatic-input-grab = 0

FIXME: On OS X, cursor movement is currently not received by FS-UAE when
the window is not focused (either something SDL 2 or OS X itself does).
This makes mouse integration on OS X a bit less useful at the moment.