Feature/output vtk path from inputfile
What this MR does / why does DuMux need it:
This adds a path prefix to the name given to the output module. This way the vtk output files can be written to a different folder.
Special notes for your reviewer:
The argument path of the Dune::VTKSequenceWriter only changes the path of the vtu files, not the pvd, so it doesn't give the desired effect.