Increased the tolerance of the local Newton method for BGRa in BRGaCreepAndInitialStressAtIP_AREHS

See merge request ogs/ogs!3771

Substitute the storage of node pointer in elements by std::array

See merge request ogs/ogs!3768

# Conflicts:
#	MeshLib/Elements/Element.cpp
#	MeshLib/Elements/TemplateElement.h

This change makes it possible to use interface
function Element::getNode() in Element::addNeighbor
function.

This remove one dependencies on _nodes pointer C array.
If all dependencies are removed the memory for storing
the nodes can be in a std::array.

New stationary creep model for rock salt

See merge request ogs/ogs!3745

[PL/CT] Implementation of look-up table approach

See merge request ogs/ogs!3744

TH2M PTM generalized initialisation for phase transition models

See merge request ogs/ogs!3770

[MeL/IO] XDMF: Fix missing header

See merge request ogs/ogs!3769

Günther Salzer Model

See merge request ogs/ogs!3747