component conferences: fix session management and init: - jingle session management is now correctly handled, with id of the Galène client used as prefix when necessary. - Galène is now run only when component session is started, avoiding systematic run on __init__. - Galène ICE logs are displayed with high verbosity. - Fix disco identity handling rel 447

these certificates are used for demo purpose only. Those must be the same as in
backend_e2e (they are generated there)