[navstik] Added a new board

Navstik STM32F4 autopilot.
This has the basic support for all the sensors and outputs most autopilots have. Still having issues with the i2c at boot, but seems to be a problem with STM32F4 autopilots.

https://wiki.paparazziuav.org/wiki/NavStik
http://www.navstik.org
Is this solving the bind issues on all boards ?
It should have been in a separated pull request, but if it is working and as the rest looks fine, I guess it is ok to keep it there.