SRVCC: Add support for incoming call SRVCC

Transfer connections from ringing call to handover call on getting
Handover Complete notification. This allows for accept to be done
on the default phone instead of IMS phone after SRVCC. Set the
state of ImsPhoneCall object to Idle after the transfer.

Change-Id: I09cfcc9fc99b3ea4b3a4bd332af546bcfae4b679
CRs-Fixed: 737743