ConnectionParticipantRole can store reference to StatusChangedSignal.
Add DestroySignal to ParticipantCore and delete instance of ParticipantCore after deleting last role.
Drop ParticipantCores::erase() and handle newly added DestroySignal.
Implement Service::on_participant_core_destroy_callback().
Update comments in ConnectionParticipantRole.
Update formatting of Identity header.