sensors: add baro calibration and cleanup

- sensor_baro.msg use SI (pressure in Pascals)
 - update all barometer drivers to publish directly and remove PX4Barometer helper
 - introduce baro cal (offset) mainly as a mechanism to adjust
relative priority
 - commander: add simple baro cal that sets baro offsets to align with
GPS altitude (if available)
 - create new sensors_status.msg to generalize sensor reporting

src/modules/ekf2/EKF2.hpp

@@ -219,6 +219,7 @@ private:
 	float   _wgs84_hgt_offset = 0;  ///< height offset between AMSL and WGS84
 
 	uint8_t _accel_calibration_count{0};
+	uint8_t _baro_calibration_count{0};
 	uint8_t _gyro_calibration_count{0};
 	uint8_t _mag_calibration_count{0};