Check the existance and versions of necessary modules when starting synapse, log which modules are used

Don't perform the check in auth.is_host_in_room but instead do it in _do_join
and also assert that there are no m.room.members in the room before doing so.

The simple fix doesn't work here because room creation also involves
unknown room IDs. The check relies on the presence of m.room.create for
rooms being created, whereas bogus room IDs have no state events at all.