UAV Outback challenge improvements from Team Swiss Fang

This is the collection of improvements done by the swiss team at the outback challenge. Needs validation / polishing.

@thomasgubler A merge with master would be great, I got confused by the (only two!) conflicts.
@AndreasAntener You changed this here: https://github.com/PX4/Firmware/commit/bc23b6239c50527aa550eed3bc6f17dec15c5c97
can you comment on this?