Some small adjustments to the libinput backend:
- Query libinput_device_config_left_handed_get_default
- Write leftHanded property to config file
- When saving the touchpad scroll mode, we need to write false to all other ones. Otherwise it will always enable the upmost entry after reboot (maybe writing an enum here would be cleaner).
- Use macro for setLeftHanded(bool) and setNaturalScroll(bool)