Spot is the consumer of screensharing using a camera
input and through a proxy connection. To differentiate
which one is active, declare a source type on the
created "desktop" stream.

* feat(screenshare): support remote wireless screenshare

- ProxyConnectionService is exposed and meant to be the
  facade for creating and updating a peer connection with
  another peer, outside of the muc.
- ProxyConnectionPC wraps JingleSessionPC so the peer
  connection handling can be reused.

* attempt to make more configurable