reformulate constraint condition
Following discussions with @wouter the constraint condition should be formulated in a different way. This MR implements @wouter's suggested changes.
The translations and rotations used for average constraints are now those in the global frame.
The canonical frame now depends on the alignable position, which is used as the pivot point for the rotation.
As further step the parent frame could be used instead of the global frame.
This MR addresses issues seen when applying constraints on the shearing of the Velo modules.
Edited by Florian Reiss