added level info config option to invoke info screens from main menu

added level info config option to invoke info screens from main menu

This is a special config option to allow level sets (like the Mirror
Magic level set "classic_mindbender") to directly invoke info screens
from the main menu (which is used for "classic_mindbender" to display
the included title story on the "level set info" screens by clicking
on a global animation that looks like a book that can be opened).