Merge branch 'dune-gfe-feature/mixed-pn-solver-rebased' into 'master'

dune/gfe/mixedriemannianpnsolver.cc

dune/gfe/mixedriemannianpnsolver.hh

dune/gfe/parallel/mapperfactory.hh

dune/gfe/riemannianpnsolver.cc

dune/gfe/riemannianpnsolver.hh

dune/gfe/riemanniantrsolver.cc

dune/gfe/riemanniantrsolver.hh

problems/cosserat-continuum-cantilever.parset

problems/film-on-substrate.parset

src/cosserat-continuum.cc

src/film-on-substrate.cc

test/CMakeLists.txt

test/filmonsubstratetest.cc

test/geodesicfeassemblerwrappertest.cc

test/mixedriemannianpnsolvertest.cc