Merge branch 'feature/dg-operator' of ssh://gitlab.dune-project.org:22022/dune-fem/dune-fem-dg into feature/dg-operator

problem wrapper.

Merge branch 'feature/scaling-limiter' into 'master'

Scaling limiter from Shu et al.

See merge request [!3]

  [!3]: gitlab.dune-project.org/dune-fem/dune-fem-dg/merge_requests/3

Merge branch 'feature/scaling-limiter' of ssh://gitlab.dune-project.org:22022/dune-fem/dune-fem-dg into feature/scaling-limiter