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
adjusted sequence of layers in dialog and LayeredVolume
removed double const
fixed implicit conversion
changes based on pr comments
added time measuring for subsurface mesh construction
moved node construction for new layers to base class
added documentation for new method
added include
Merge pull request #528 from rinkk/SubsurfaceDemConflict

[Fix] Subsurface DEM Conflict