UrfConfig: add get/set_prev_soft functions

Add a prev-soft flag which is used to track the state of a
killswitch before flight-mode is entered.
UrfDaemon: current state before flight-mode actions

Check the current flight-mode state before actually
calling urf-arbitrator_flight_mode().  If the desired
state is the same as the current flight-mode state,
then just return a successful DBus result.
UrfDeviceOfono: make bus connect synchronous

A UrfDeviceOfono instance is only created once ofono
is detected on the bus.  This change makes the proxy
creation synchronous which allows property changes
to be handled directly.
UrfKillswitch: changed blocked param to block

This change makes urf_killswitch_set_software_blocked()
parameter naming consistent with UrfArbitrator's convention.
[WIP] UrfArbitrator: more syncrhonous changes