fix showing mp_connect between sp scenarios

show_connect ("configure sides" in advanced settings dialog) is now carried over between scenarios, and is used to determine whether to show mp_connect between scenarios. it is used as the default value of allow_new_game_flag, so setting allow_new_game in config will override show_connect for scenarios after the first one. also, mp_connect will be shown between scenarios regardless of settings if debug mode is enabled (this is unchanged).