cmd_vel and odom integration for the sensorless jetbot

[GavinKane]

Pull request creates a differential drive controller, with the motor control inside a hardwareinterfface class using Tom Clarks cpp version of the ADAfruitMotorHat. It allows /mobile_base_controller/cmd_vel messages to be recieved by jetbot, and robot will be able to provide odom messages back. Odom is provided through dead reconing, whích for a robot without any sensors on the motors, is the best we can do. If the robot is moving fast, it works well. If the robot is trying to move slowly, near the dead-zone of the motor, it is not very accurate. But working with AMCL it is good enough to maintain a track of its position in a given map. Best not to run AMCL on the Jetbot itself, but on a separate computer.