- Add callback to notify the application that a participant has changed role in the conference
  - Take into account role when creating the list of participant informations of a conference
  - Give priority to the conference information stored in the database over that cached in the call log object
  - When a participant is added, give the application a pointer to it with all the informations up to date
  - In the event of a full state, reduce the number of database accesses by updating the conference information in the callback onFullStateReceived. Previously, for every participant added a DB access was required in order to update the conference information

Tests:
  - Add verification of role and sequence id of every participant info in the conference information in the call logs and conference information
  - add helper functions to ease checking of conference informations