[doc] documentation for the updated classes

[doc] documentation for new keywords

[doc] documentation for prj_com_property

[base] update classes for ogs v6.4.1

[base] added class arguments for new keywords

[tests] skip benchmarks with *.xml project-files

small test for directory without any *.pvd files

    paths to referenced files in the PRJ file have to be relative
    to the PRJ file

   before the complete config was replaced by the cfg file
   now, only specific options defined in the cfg file are updated

Tests that make sure the function only accepts valid r2ogs6 components in the right format

    set ogs executables explicitly instead of ogs bin folder path
    add option to use ogs singularity containers