Further handover support changes.

Add handover extras key used when initiating handover.
Add handover complete / fail connection events which are sent to the
initiating IncallService when a handover is complete or fails.
Adding PhoneAccount extra to indicate that a self-managed CS should have
its calls logged to the call log.

Test: Manual
Bug: 37102939
Change-Id: Icbb6f1addf913de841a9c48089a7d8311668f3bc