Migration to new SDP format

LiveLab is currently broken because it relies on the same remote and local track IDs to coordinated between remote and user media. Starting this issue to track migration to the new SDP API, as documented at https://docs.google.com/document/d/1-ZfikoUtoJa9k-GZG1daN0BU3IjIanQ_JSscHxQesvU/edit

Example at: https://webrtc.github.io/samples/src/content/peerconnection/pc1/