`apply_aero_z_offset!` directs the offset along the body-frame

[ufechner7]

This is a bug. The purpose of this offset is to stabilize the wing, which works best if applied along the z-axis of the principal frame.

[1-Bart-1]

This is not true. The aero z offset is made to stabilize the wing rotation around it's local y axis such that the local z axis is closely aligned to the (elevation, azimuth) of the kite. The principal frame z axis can have any rotation around the local y axis, and is therefore not reliable for this.