- only SENSOR_POLLRATE_DEFAULT is needed

 - only used in self tests

- set integral states and setpoint of reference state to 0
- set thrust to NAN if it will be computed from position and velocity control

added unseal() and seal() around write_flash() for enabling/disabling cell undervoltage, we found out today this wasn't being written because that address is in protected flash

commented out something causing trouble with CI, it is in an unused function but I'd like to keep the comment there as a reference for future development effort