High-Res Menu Scrolling (Patreon)

Been improving the menu scrolling functionality in the menus that uses it.

The scrolling of the Key Configuration menu works properly now, and I've implemented high-resolution scrolling in the Single Player Maps menu.

The scrolling algorithm in the Single Player Maps menu is more robust than the one used in the other menus, and will serve as a base for a general-purpose scrolling algorithm for all menus.