[untracked] implemented service channel b/w consumer and producer

- any metadata can be now distributed using ServiceChannel instance in
SessionInfo structure
- currently, only meta info about ongoing media streams and their
encoding parameters is published
ref #1928 [implemented external capturer in library]
test-chrono-chat: using default keyChain
Merged with alpha5
ConferenceDiscovery: passing defaultKeyChain into FaceProcessor