Added SteeredWheelBaseController::stopping(), which is called when the
controller is reset, for example when the E-stop is deactivated.
stopping() stops wheel motion. SteeredWheelBaseController::starting() no
longer initializes the transform from the odometry frame to the base frame,
so activating then deactivating the E-stop no longer makes the odometry system
think that the robot has moved to the origin of the odometry frame.