Added delay

Depends on #7050,
allows the admin to specify a delay for observers.

P.S. This delay does not apply to the admin if he is a spectator simply because that would screw up the AI completely.
This is occupying the same space that the difficulty dropdown is using (in TD, too).

Also, as a user, I'd have no idea what kind of input is expected there. I feel a dropdown with a few sensible choices would be better.