Add PID support for Talon SRX and Jaguar motor controllers #40

We're going to add hardware-based PID control. This will largely be via our existing Controller interface, which PIDController implements and which a new TalonController interface extends and exposes all of the real Talon SRX CAN PID functionality. A HardwareTalonController implementation class will directly use the wpilibj.CANTalon instance, will have a no-op Executable, and will be created via the Hardware class.

See the following class diagram.