gw: Assign owner to new registered devices
gw: Assign owner to new registered devices

This patch extends 'signup' for HTTP/REST assigning owner when a new
device is registered to Meshblu.

CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source