Added "Quit Application" button to pause menu. Set menus to disabled by default if they got disabled by default

Couldn't bear the visual clutter in the editor, and having to go back to the launch menu.
Opening those prefabs caused Unity to change a whole lot of other prefabs and assets as well. At least some of those changes are strings getting surrounded by quotes, but for most others I have to guess option names changed in Unity 6. Gonna commit all at once, because I don't want to accidentally break something if a specific combination of changes shouldn't work.