Reduces generated tokens and session ids down to 32 characters (~190 bits of entropy) in length

Raise 404 "Room not found" when changing or accessing room visibility
settings (`GET` and `PUT
/_matrix/client/r0/directory/list/room/{roomId}`).
See issue #290

Allows Conduit users to join restricted rooms if we are not currently participating

Rejoin room over federation if we are not participating in it; do not include invited users in participating servers calculation

Now we start the admin and sending threads at a later time.