Add functions sol.menu.bring_to_front/back()
Add functions to bring menus to front or back: sol.menu.bring_to_front/back(menu, [other_menu])
If other_menu is nil, menu would be put in front/back of all the other menus with the same context. If other menu is given, then put menu immediately as the next menu in front/back of it.
Remark: We need this feature for the rain script of the project Children of Solarus (the rain manager uses a menu, and we do not want the rain to be drawn above the inventory menus, hud, etc).