add an `autokick after 5 minutes` feature

[redianthus]

Hi,

It would be great to add a variant of the autokick when there's no more op feature which would autokick everyone after e.g. 5 minutes since the last op left the room.

This is useful in case the op has to restart its browser or its computer.

Cheers,

[jech]

I think it's a good idea.