AP_AHRS: re-run update_trig() after EKF AHRS update
GCS_MAVLink: added POWER_STATUS message
GCS_MAVLink: rebuilt MAVLink headers
GCS_MAVLink: added send_power_status()
DataFlash: added power status logging
AP_HAL: added servorail_voltage and power_status_flags() API on AnalogIn
Plane: log power status on Pixhawk
Rover: log power status on Pixhawk
Copter: log power status on Pixhawk