Add crouching, update example, better sane defaults, minor fixes

[qhdwight]

• Add crouching
• Crouching prevents controller from falling off a ledge
• Use system sets to force defined update of all fps systems
• Added a new feature "friction_normal_cutoff" that may make surfing possible 👀
• Saner defaults, for example max air speed was lower than running and sprinting
• Make example use zero friction and restitution since we handle that in controller
• Change colors of example scene to be better