[Config] Toggle mouse visibility

[PxlBuzzard]

This is the first step towards supporting custom (or no) cursors in a game. We should eventually have a game script example showing how to add custom cursor graphics.

Display:
    Cursor: false

[ColdenCullen]

I think this is super important, but it would probably be better to do through code. Most menus would need the cursor to be visible, and I don't like the idea of setting value in YAML that would also frequently change though code as well.