Implement PIDSourceFromTalon

[brettle]

We need to be able to read the distance and rate from the encoders when they are connected to the Talon instead of the RoboRio. Create a class PIDSourceFromTalon that implements PIDSource and can be used to read the rate or the distance from an encoder that is attached to a Talon.

[brettle]

Implement PIDSourceFromTalon