move to 30hz fast rates

[aedsinger]

This PR updates the default control rates to the Joint Trajectory Action Server to 30 Hz. It:

• Presumes that Stretch Body is upgraded to 0.5 and the firmware to P3 (as these updates support the faster control rates).

• Modifies where push_command is called such that it is only called in one place (avoiding a race condition where two calls too close together can violate the Pimu's trigger_motor_sync limitation on rates)

• Disables the status_thread in the Robot class of Stretch Body (and instead is updated by the ROS thread).

[hello-binit]

Thanks, I'll review this soon.