Uninvited participant role:

- Speaker -> participant has been added by an admin through a REFER
          -> participant has called the conference and all other participants are speakers
- Listener -> participant has called the conference and there is at least a listener being part of the conference

Look if there is a conference info matching the to address in the database in order to know if a call will be part of a conference even if the call cannot be started right away if ICE candidates have to be gathered firt

Wait for the call to onFullStateReceived before updating the conference informations when parsing a NOTIFY full state. This allows to optimize database accesses