The refactorization is the first step to also partition PropertyVectors by the same schema.

Fix Hex20 shape functions; Add partition of unity tests.

It is used by more than few tests now.

[PL] Add output of darcy velocity to RichardsFlow process.

Implements the computation of darcy velocity as a seconday variable based on the pressure values of the current time step.

[Conan] Temporary fix mac conan issues related to Qt package.

The Qt package was rebuild and misses some symlinks inside its
*.framework/-directories which leads to an error in copying these
files. Temporary disable copying.

Cleanup: Clang format, fix spelling, remove debug code, ...