Rotorcraft: Floating point euler stabilization

Based on pull request #419

The aim is to provide a reliable floating point control (euler based). With standard integer control I most likely experienced a loss of precision (one of the scaling constants), which affected the control performance. Once I finish this I will post some comparison.

This is the first step:
Added xml file for Turnigy_9XR radio
Fixed failsafe descend rate setting in autopilot.c
Added interface between floating point stabilization and integer navigation/guidance
Added safety feature - AP stays in kill mode until it gets valid data from AHRS (modified ahrs_aligner)

Please read comments in the code and give me your opinion on that.

Second step: 
upload clean version of stabilization_attitude_euler_float.c with gain scheduling.