Remove periodic grids

See merge request !163

This was never used, and it is of no interest to Dune.
So let's remove it.

Fetch default yml files via different project instead of url

See merge request !161

This is a workaround for a bug that showed up after gitlab migration. See issue
infrastructure/issues0#62 for further discussion.

Merge branch 'feature/require-cmake-3.13' into 'master'

See merge request [!158]

  [!158]: Nonestaging/dune-uggrid/merge_requests/158

Merge branch 'remove-evalproc' into 'master'

See merge request [!157]

  [!157]: Nonestaging/dune-uggrid/merge_requests/157

It is not used.

The flags have been removed from the code a while ago.

It was used to distinguish headers that were internal
to UG.  However, today all code in dune-uggrid is
internal to the Dune grid interface, and therefore
the old distinction is not needed anymore.

Merge branch 'remove-directory-numerics' into 'master'

ref:staging/dune-uggrid\> It is not used anymore.

See merge request [!156]

  [!156]: gitlab.dune-project.org/staging/dune-uggrid/merge_requests/156

It is not used anymore.

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.