Update conference call APIs.

Clean up conference call APIs to use a distinct type separate from
Connection.  Also allow the addition of Conference calls at any point
using addConference() API method.

Bug:16844332
Bug:16449372
Change-Id: I34e45fde1aa43559f5f4e29b990929c188b16875

telecomm/java/android/telecomm/RemoteConnectionService.java

@@ -135,7 +135,7 @@ final class RemoteConnectionService {
         }
 
         @Override
-        public void addConferenceCall(String callId) {
+        public void addConferenceCall(String callId, ParcelableConference parcelableConference) {
             // not supported for remote connections.
         }