provide dashboard for room full + camera during the event

[johanvdw]

Ideallly we can integrate these into pretalx, at least we should link them from pretalx.

Not sure where this is exactly documented, but most code lives at: https://github.com/FOSDEM/infrastructure/tree/6119172c1d7f6057cec5818417d1acf69501edcc/ansible/playbooks/roles/video-control-server