Merge branch 'VariableOutput' into 'master'

MeshLib/IO/VtkIO/VtuInterface-impl.h

MeshLib/IO/XDMF/transformData.cpp

MeshLib/PropertyVector.h

MeshLib/Vtk/VtkMappedMeshSource.cpp

ProcessLib/LiquidFlow/Tests.cmake

ProcessLib/Output/Output.cpp

...x1_SteadyStateDiffusion/cube_1e3_calculatesurfaceflux.prj

...yStateDiffusion/cube_1e3_neumann_calculatesurfaceflux.prj

...yStateDiffusion/cube_2e3_prism_surfaceflux_front_back.prj

...yStateDiffusion/cube_2e3_prism_surfaceflux_left_right.prj

...yStateDiffusion/cube_2e3_prism_surfaceflux_top_bottom.prj

...dyStateDiffusion/wedge_1e3_prism_surfaceflux_diagonal.prj

Tests/Data/HydroMechanics/A2/A2.prj

...ata/HydroMechanics/ExcavationNiches/excavation_niches.prj

...ta/HydroMechanics/ExcavationNiches/excavation_niches2.prj

...FailureIndexDependentPermeability/quad_with_half_hole.prj

Tests/Data/HydroMechanics/GroundEquilibrium/simHM_ground.prj

.../HydroMechanics/GroundEquilibrium/simHM_ground_python.prj

...HydroMechanics/GroundEquilibrium/simHM_ground_quadBCu.prj

...chanics/GroundEquilibrium/simHM_ground_quadBCu_python.prj