Added SpeedControllerMultiplexer class.

This class will be used to multiplex SpeedControllers and allow us to fake
multiple SpeedControllers to the RobotDrive class.
Added new constructor and method to Drivetrain class for Multiplexer.

The new constructor takes in 8 integers for each CANJaguar and contructs
them using the SpeedControllerMultiplexer. Encoder usage has also been
removed.
Modified Drivetrain initialization to also use MINI Jaguar constants.