[gmsh] (optionally) writing physical curves to gmsh geo output
Small extension of the GMSH Interface (for the AREHS project):
It's now possible to explicitly write physical group information into the GMSH geo-file.
The additional information will only be written, if a specific flag is set. Currently, only the VerticalSliceExtraction
tool uses this functionality.
(Checked with @dominik-kern that this is actually what he needs.)