Merge branch 'ci/centralize-config-2.6' into 'releases/2.6'

See merge request [!30]

  [!30]: Nonecore/dune-grid-howto/merge_requests/30

Merge branch 'feature/require-cmake-3.1' into 'master'

See merge request !24

[cmake] Require CMake 3.1 similar to dune-common

See merge request !23

(cherry picked from commit 1a5b10cf)

daef87f6 [cmake] Require CMake 3.1 similar to dune-common

Merge branch 'bugfix/cmake-install-executables-as-targets' into 'master'

See merge request !21

[bugfix][cmake] install executables as targets

See merge request !20

(cherry picked from commit e419e504)

055fa455 [bugfix][cmake] install executables as targets

.gitlab-ci.yml: build against releases/2.6 branch of other modules

See merge request !18

[ci] stop testing with Debian 8

See merge request !16

use `std::array` instead of removed `Dune::array`

See merge request !17

This way dependencies installed via `duneci-install-module` are built
with the same options as the module to be tested.

Use new MCMGMapper interface

See merge request !15

Reference: dune-grid!177

.gitlab-ci.yml: update environments

See merge request !14

- Added:   Debian 10 with gcc in C++17 mode
- Removed: Debian 8 + Backports with clang

Reference: http://lists.dune-project.org/pipermail/dune-devel/2017-July/002224.html

[Fix] Update mailing lists addresses.

See merge request !13

Change module version number to 2.6-git

See merge request !12

Install dune-uggrid before dune-grid

See merge request !11

* update list of contributors
* replace README by README.md
* replace COPYING by LICENSE.md
* create symbolic link from COPYING to LICENSE.md
* cleanup .gitignore

This doesn't look elegant to me, but at least it works for now.
It might be better to just use YaspGrid directly in the future.

Fix/doc latex create doc install

* Replace deprecated arguments in dune_add_latex_document
* Fix call of create_doc_install to new signature

See merge request !8

After the merge of dune-common!115, we have to specify the cmake
target which builds the pdf in `create_doc_install`.

Feature/remove old alugrid



See merge request !7

We only support dune-ALUGrid

Adjust exception handling in tests.

Dune::Exception is derived from std::exception.

See merge request !4