Feature: Video "chat"

Unlike casting (#3) technology should scale only for some limited number of participants. Primarily oriented toward presentations to small'ish groups (poster, break-out room, etc).

- possible to "cast" (#3), i.e. to take mix-in as a video source for casting to . Check how debconf (see #3) system does it.
- possible for participant(s) to share the screen.
- integratable with chat (#4), Q&A (#11 ), notes (#6 )

- jitsi -- open, peer-to-peer, no (much) burden on the server.
- http://www.sparkle.space/ . Code: https://github.com/sparkletown/sparkle -- yet to grasp potential