Allow User to join from list of current meetings

[spoorun]

1. User opens the Jitsi Meet app within Humhub
2. As well as starting a meeting, they can see a list of current meetings in their Humhub network (except any meetings marked private)
3. They can click to join an existing meeting (either directly, or through a waiting area as per settings for that meeting)
4. Admin can turn off this feature in settings

[Lyamc]

I think this would be a nice-to-have so people can quickly join a meeting with someone else, so long as they have the password