Merge branch 'remove-more-unused-stuff' into 'master'

See merge request [staging/dune-uggrid!153]

  [staging/dune-uggrid!153]: Nonestaging/dune-uggrid/merge_requests/153

Instead, we let the multigrid store them directly.  That is
much simpler.

Apparently they were not used at all

And remove lots of code that we never actually exercise.

Our format does not use type options.

The remaining commands are not needed anymore: The parts of them
that dune-grid needs have been merged into dune-grid.

They are not used.

Merge branch 'dune-2.7-toolchain' into 'master'

ref:staging/dune-uggrid\> In particular, the Dune core now practically
requires C++17, and therefore all test scenarios with C++-14 need to be
removed.

See merge request [!154]

  [!154]: gitlab.dune-project.org/staging/dune-uggrid/merge_requests/154

In particular, the Dune core now practically requires C++17,
and therefore all test scenarios with C++-14 need to be
removed.

Merge branch 'feature/refactor-recursive-coordinate-bisection-lb' into 'master'

ref:staging/dune-uggrid

-   Use more descriptive variables names and comments
-   Use some descriptive helper functions
-   Reduce code duplication
-   Improve sorting efficiency by using only a partial sort with
    std::nth_element
-   Define variables in local scope
-   Remove doc clutter

See merge request [!151]

  [!151]: gitlab.dune-project.org/staging/dune-uggrid/merge_requests/151