Standard GPS setup (raw/nmea) will both enable the GPS module and take full
control of the GPS port. This prevents other processes from reading the NMEA
traces from e.g. a tty. In order to handle this, a new 'unmanaged' GPS location
source is introduced, which will just enable/disable the GPS module, without
reading anything from the GPS port. Of course, both raw/nmea and unmanaged
setups cannot be enabled at the same time.
