GUI Scrolling Improvements (Patreon)

Added support for Page Down, Page Up, Home and End keys to the Single Player Maps menu, and fixed a few issues with the scrolling of the list of maps. It really works great now.

This list scrolling algorithm will be used in the new menu system I'm designing.

And now I'm also adding support for Page Down, Page Up, Home, End, Ctrl+Home and Ctrl+End keys to the text viewer. As soon as it's finished, I'm releasing the next version.