fixed issue where dem nodes could be located below mesh bottom in prism meshes
correctly cleared reserved mem again
resolved dem-nodes below bottom layer for tet mesh generation

Conflicts:
	MeshLib/MeshGenerators/LayeredVolume.cpp
removed double const
changes based on pr comments

Conflicts:
	MeshLib/MeshGenerators/LayeredVolume.cpp
moved node construction for new layers to base class
added documentation for new method
added include
changing the sequence in which rasters are read for tet meshes from low to high
Merge branch 'data-explorer-5' of https://github.com/ufz/ogs into data-explorer-5