Feature/update poro and perm laws

WIP: The actual correction/renaming of the misleading functions and variables initialP(orosity/ermeability) to referenceP as suggested in #433 (closed) is finished and this can be merged. However, the 2pncmin tests do not pass, just as they did not before on master. I already renamed a few variables in the reference solution according to the new names in the vtus and updated the vtu number which is compared to the reference, but still the same, or at least very similar, value differences as in the master versions remain when comparing reference and test results for 2pncmin.