Merge branch 'feature/nonlinear-sumfact-cg' into 'master'

ref:dominic/dune-perftool Contains [!264] and master\....

See merge request [dominic/dune-perftool!269]

  [!264]: gitlab.dune-project.org/NoneNone/merge_requests/264
  [dominic/dune-perftool!269]: gitlab.dune-project.org/dominic/dune-perftool/merge_requests/269