- #10359

added a check to ensure the initialize settings function succeeds. If it does not, the driver fails gracefully. This handles the case that the device is not there.

 * tested on SPI (px4fmu-v4pro)
 * WIP I2C support

Failure Detector - use bitmask field instead of boolean in vehicle_status msg (failure_detector_status) and instead of struct in class

Failure Detector - move "force_failsafe" flag inside circuit_breaker protection; remove PX4_WARN and send mavlink msg only once

- use pragma once guard in FailureDetector.hpp
- send Commander parent to ModuleParams and remove update_params() method
- simplify attitude checks
- FailureDetector::get_status() (previously named "get") is now a constant method that returns a constant reference

NullMixer - Send NAN instead of 0. NAN is mapped to disarmed in fmu and io. A Null mixer can now be used to set a fixed value: "disarmed" if the system is operational or "failsafe" in failsafe mode

FailureDetector - Add check for non-zero roll/pitch failure parameters. Rename 'result' into 'updated'

FailureDetector - New class, first working simple implementation. Outputs PX4_ERR messages if roll or pitch is exceeded.