Add back in-call vibration features (1/2)

Add backend implementation, implemented in UI instead of telephony
service this time.

Change-Id: I39ccc423d3d38b0dd78b4e291a2ec2ef679cd865
Fix call tracking.

getActiveCall() can return null when ending calls locally before they
are answered locally, so better use the presence of an active call as
indicator of whether to do the vibration instead of using the state.

Change-Id: I088cd743c9a9e6704e93f8c48fb566b3a20ca8be