CoG of retracted landing gear

[MarAlder]

Reposting a question from @0bernd in #764:

If a landingGear is retracted the landingGear CoG is different, how to work with this issue? Normally, I would calculate the LG CoG distance to the attachment point and move it along the rotation axis. But this information might be useful to store in the cpacs dataset. Especially, a more detailed LG is used in which more movable elements are, then the CoG change is not only along the rotation axis. And if I am only interested in the CoG of retracted and extended LG and not to the whole LG kinematic etc. it might be make sense.