Chatapp webrtc

Tests and implementation of WebRTCCall model and chat, as well as further advancing of the chat application.  Parts paired with @tOkeshu, parts solo on both sides.  A particularly good way to land, I suspect, would be for @n1k0 and @tOkeshu to pair-review.  Though maybe @n1k0 would prefer to just do the usual github PR annotation process...