Add encoder to DriveSubsystem

[michaelvdow]

There should be an encoder for each side of the robot. It needs to be initialized using port numbers from the RobotMap class.

Methods to create for each encoder (____ = Left or Right):

• get____EncoderCount()
• get____EncoderDistance()
• get____EncoderRate()
• reset____Encoder()

Check this link for more help: http://wpilib.screenstepslive.com/s/4485/m/13809/l/599717-encoders-measuring-rotation-of-a-wheel-or-other-shaft

[gabrielbryk]

Did research and as far as I can tell the code is the same for CAN vs PWM