pScrewAxis

I'm not so sure about the minus sign for pScrewAxis in the joint constructor. Can someone explain, e.g. @gchenfc or @yetongumich ? The Adjoint formula does not have a minus sign. I know test break, but only a few are "real", others seem to be self-fulfilling prohecies.

Start by locating the joint constructor and the pScrewAxis handling, then compare its sign convention with the Adjoint formula. Run the affected tests and separate genuine failures from self-fulfilling expectations. Done means the intended convention is established and the implementation and tests consistently reflect it.

Written by the indexing model from the issue text.