UrfArbitrator: always set device state to the saved state in persistence
UrfArbitrator: properly call urf_arbitrator_add_device in add_killswitch.
UrfArbitrator: make sure kernel devices are only added to the devices list once
UrfDeviceOfono: try to set Online for the modem to what we want it to be whenever Powered changes.
bugfix: remove unused variable priv in urf_config_dispose and urf_arbitrator add_killswitch
UrfDevice: make the device registration and properties more generic
UrfDeviceOfono/UrfDeviceKernel: use the new way to call urf_device_register_device to register DBus, and only show specific properties.