Add a script that calculates the rotational inertia around each of the three axis

[ufechner7]

Currently the inertia is defined by the mass distribution, but it is nowhere explicitly calculated. Doing this would make it possible to match inertia values obtained from a CAD model.

[ufechner7]

Suggestion:
To define the matrix of inertia, use:

• All kite points + KCU at using the unstreched bridle line lengths as distance from one another
• Centered around the CG of these points