Added possibility to switch sticks
Merge pull request #440 from EwoudSmeur/switch_sticks

Added possibility to switch sticks

The reason for this commit is that the sticks in rate control are 'quadcopter sticks'.
This is because the default (IMU_TO_BODY) configuration is hover.
The only way to get the sticks naturally right is to have the BODY_TO_IMU
orientation as airplane.
The easier way is to just switch roll and yaw when in rate control,
if the user defined this in his airframe of course.