Make SubscriberNumbers writable.

Make SubscriberNumbers writable.

This implements writing SubscriberNumbers if the SIM allows this
(optional to the SIM provider).  Because the property is an array
of phone numbers, setting the property needs to write multiple
records on the SIM so it's not atomic and potentially can fail
partially.  In this case we have to report a write error to DBus
client but at the same time file may be changed and we send a
PropertyChanged.