newaccountmodel: registered name for SIP account

After updating SIP account profile, account URI disappears from
select account widget because registered name is the same as a
display name.
This patch set registered name empty when update account from
configuration properties because SIP account does not have
registered name.

Change-Id: I8ce9a98e390328e2a9a9404bf8c079547adc9ca3
Reviewed-by: Andreas Traczyk <andreas.traczyk@savoirfairelinux.com>