Option to hide the number of participants / hide "nobody's going"
Event organizer must be able to choose to manage participants on Mobilizon or not. If not, they need to be able to hide the number of participant.
This has been developed on events.htu.at for instance:
cf https://framacolibri.org/t/using-mobilizon-for-regional-leftist-subculture-calendar-platforms/18772