Finalize multiendpoint functionality.

1) Handle the PULLING state throughout telecom.
2) When parcelling calls to send to InCallServices, remap PULLING state
to DIALING if an InCallService doesn't support external calls.  This
ensures compatibility for things like Android Wear/Auto.
3) Ensure add call isn't disabled because of external calls.
4) Modify InCallController to handle changes to whether a call is external
or not.  For IncallServices that do not support external calls, we will
add the call when an external call becomes a regular call, and we will
remove it when a regular call becomes external.

Change-Id: I1bf6c1f7e182834c3ab1ed34cd119467a4698993