Example of PID Tuning Using Only Smart/Shuffleboard Get/Sets

[MC42]

While the current docs show off using the PID widget in Shuffleboard, that example relies on the WPILib PIDController object. There's no example for quickly changing on-robot variables used elsewhere other than specifically the PID widget, and adding one would enable teams to port the concept to tuning other mechanisms without needing to redeploy robot code.

[Starlight220]

Actually, it might be better to wait until the NT4 rewrite, as doing this listener-based is more appropriate than get/sets.