Current construction of rib geometry sometimes leads to non-planar ribs.

[AntonReiswich]

The current construction of the geometry of a rib allows ribs to be non-flat.

This is not intended as for example shows in the error message thrown in CCPACSWingCell.cpp within the function body of CCPACSWingCell::CutSpanwise.

The reason for this:
The function CCPACSWingRibsDefinition::BuildRibCutFace can return a non-flat face, since its construction is based on an interpolation of potentially windswept wires (local variables within the function's body: cutFaceFrontWire and cutFaceFrontWire).
The reason why these wires might be windswept, lies in the fact that the vectors used for its construction, that are handed over to the function CCPACSWingRibsDefinition::BuildRibCutFace via the arguments upVecStart, and upVecEnd, are constructed with the function CCPACSWingRibsDefinition::GetRibUpVector in an incorrect way: the problem with this function is that its local variable cutPlaneNormal is a vector that might have different directions at the first spar and the last spar.