Fix rotation

Reported on https://github.com/AutonomyLab/ardrone_autonomy/issues/113 was causing reversed axes issues with the robot_localization package.

Also keep the magnetometer data published even if the readings are stuck.
You are welcome. I fixed the RPY bug in upstream repo. I do agree that even when the magnetometer is stuck, it's better to send the value. However, div/zero should be handled properly.