edge: add RTCDTMFSender alias
edge: add RTCDTMFSender alias

adds RTCDTMFSender if it does not exist. Its a simple alias to
RTCDtmfSender as described in http://draft.ortc.org/#rtcdtmfsender2*

webrtc/adapter,Acidburn0zzz/adapter,webrtc/adapter,Acidburn0zzz/adapter,Acidburn0zzz/adapter