show "only one player must enter exit" config option on exit elements

[ncrecc]

in the editor, the "only one player must enter exit" option in the config for players 1-4 should also be in the config for the relevant exit elements:

• exit_closed
• exit_open
• em_exit_closed
• em_exit_open
• steel_exit_closed
• steel_exit_open
• em_steel_exit_closed
• em_steel_exit_open
• sp_exit_closed

(the sokoban object/field elements when "exit level if all tasks solved" is checked are not relevant, since the level will always be successfully exited upon completing the sokoban tasks if that is checked, regardless of dead players or the state of the "only one player must enter exit" option.)