Issue 191: RTCIceTransport cannot go to "completed" state

>From Robin Raymond:
https://github.com/openpeer/ortc/issues/191

Robin's suggested fix:

On the RTCIceGatherer.onlocalcandidate, we should include:

When the final candidate is gathered, an RTCIceGatherer.onlocalcandidate event occurs with a RTCIceCandidateComplete emitted.

On the RTCIceTransport.addRemoteCandidate, we should include:

When the remote RTCIceGatherer emits its final candidate, the local RTCIceTransport.addRemoteCandidate should be called with an RTCIceCandidateComplete dictionary being passed in so that the local RTCIceTransport can know there are no more remote candidates expected and the local RTCIceTransport can therefor go enter into the completed state.