Merge branch 'allow_no_vtk_output' into 'master'

CHANGELOG.md

README.md

dune/copasi/common/CMakeLists.txt

dune/copasi/common/bit_flags.hh

dune/copasi/common/enum.hh

dune/copasi/local_operator/diffusion_reaction/multidomain.hh

dune/copasi/model/diffusion_reaction.cc

dune/copasi/model/diffusion_reaction.hh

dune/copasi/model/multidomain_diffusion_reaction.cc

dune/copasi/model/multidomain_diffusion_reaction.hh

test/CMakeLists.txt

test/test_no_writer.mini