update webrtc/MediaStream.d.ts, RTCPeerConnection.d.ts

Update for Firefox Support

RTCPeerConnection.d.ts
 - update Window Interface
 - add webkitRTCSessionDescription, mozRTCSessionDescription, webkitRTCIceCandidate, mozRTCIceCandidate
 - append semicolon at the end of "declare var" sentences.

MediaStream.d.ts
  - add mozGetUserMedia
  - append semicolon at the end of "declare var" sentences.

Usage Sample: https://github.com/nakakura/WebRTC-sample