Camera-IMU triggering and synchronisation message.

                time_usec                 : Timestamp for the image frame in microseconds (uint64_t)
                seq                       : Image frame sequence (uint32_t)

def camera_trigger_send(self, time_usec, seq, force_mavlink1=False):
                '''
                Camera-IMU triggering and synchronisation message.

                time_usec                 : Timestamp for the image frame in microseconds (uint64_t)
                seq                       : Image frame sequence (uint32_t)

                '''
                return self.send(self.camera_trigger_encode(time_usec, seq), force_mavlink1=force_mavlink1)