skip crafters with high load

at the same priority, don't add to crafters which have a large load.

eg: you request 200 items, and a crafters have 500, 200, 200 todo, it
will skip the 500.

(criteria is skip crafters with todo of < min(load)+request/2 ; if that
fails, use crafters with todo< min(load) +request.
and the interface update.