Implement host side torque control

[ugocupcic]

Reuse the code from position controllers, takes torque demand, computes pwm using PID. Clamps torque between 0 and 1 (using parameter server and sr_ethercat_hand_config yaml file).

@jlaforga needs it quickly: a customer wants to be able to switch between position and torque control very efficiently.

[guihomework]

Is there a planned dev to get high speed torque reading ? Currently, I think the fastest is 500 Hz if all other motor sensors are dropped and this is quite slow regarding the higher level control loops running at 1 kHz.

[ugocupcic]

Not really for now. I was planning to try it as is and see how it behaves, then go from there.

[ugocupcic]

Iceboxed for now. There's a new beta firmware that seems to give a good torque control on the motor board, which behaves well with the position control from the host.