Add some space transitions checks

Away missions with too many space tiles would make the _setup_map_transition_ proc take too long to finish, making Byond throw a runtime, thinking there was an infinite look

* Away missions space tiles won't be processed for the space cube setting
* setup_map_transitions proc is now set to background if processing too many tiles (prevent Byond infinite loop protection from kicking in)
is this number arbitrary, or did you test for it? I'm just wondering.