Feature/mavlink update

Hi,

The version of mavlink that is currently in dune is about 2 years old, and we need some of the new messages on our end. 

**This PR is not yet ready to be merged**, since only minor tests have been done at our end to see if existing systems work as expected. Its purpose is to let you guys know that an update like this is desired, and maybe you would like to contribute in testing this. 

The version of mavlink is copied directly from the ardupilot project at the following commit: d62b9a70444f8439c2f49e76e42cbab104a4e10c

The git history for mavlink from that point and backwards can be seen here:
https://github.com/diydrones/ardupilot/commits/d62b9a70444f8439c2f49e76e42cbab104a4e10c/libraries/GCS_MAVLink

I'll update this PR when more testing is done.