Move simulator driving kinematics into motor driver plugin

[daweim0]

Right now our robot control Gazebo plugin spins the wheels of the simulated rover and then gazebo figures out how the robot should move. This does not work very well and it takes a lot of processing power (mostly because Gazebo is very CPU hungry). Move the rover kinematics into the Gazebo plugin and turn off physics for the simulated rover in Gazebo (the plugin would calculate where the rover should be and update it's position in Gazebo).