Merge branch 'bugfix/fix-broken-doxygen-links' into 'master'

ref:core/dune-grid-howto The links now point to the current unstable version
of the documentation.

I changed the link Iterator to EntityIterator because from the context I
assume that's what was meant.

Also, there is a paragraph left about EntityPointer, which are no longer there
(therefore that link is still broken even in this MR).

See merge request [!32]

  [!32]: gitlab.dune-project.org/core/dune-grid-howto/merge_requests/32

Merge branch 'feature/generate-images-from-svg' into 'master'

ref:core/dune-grid-howto Generate PNGs from SVG instead of EPS

See merge request [!31]

  [!31]: gitlab.dune-project.org/core/dune-grid-howto/merge_requests/31

It does no longer contain EPS files

Merge branch 'feature/uselatexmk' into 'master'

ref:core/dune-grid-howto Drop makeindex and printindex, as no entries are
defined and it broke latexmk.

This requires [dune-common!577]

See merge request [!28]

  [dune-common!577]: gitlab.dune-project.org/Nonedune-common/merge_requests/577
  [!28]: gitlab.dune-project.org/core/dune-grid-howto/merge_requests/28

Drop makeindex and printindex, as no
entries are defined and it broke latexmk.

Merge branch 'ci/centralize-config' into 'master'

See merge request [!29]

  [!29]: Nonecore/dune-grid-howto/merge_requests/29

Merge branch 'feature/fix-deprecation-geometry-type' into 'master'

finitelements did not work since the change to CMake as the Alberta flags were
not added.

Further a bunch of deprecation warnings got fixed.

See merge request [!26]

  [!26]: gitlab.dune-project.org/core/dune-grid-howto/merge_requests/26

See merge request !27

[cmake] Require CMake 3.1 similar to dune-common

See merge request !23

added empty changelog

See merge request !22

[bugfix][cmake] install executables as targets

See merge request !20

Installing the generated executables als `FILES` resulted in the following
error message on Debian Stretch (CMake 3.7.2):
```
CMake Error at cmake_install.cmake:44 (file):
  file INSTALL cannot find
  "/home/nolte/numerics/master/dune-grid-howto/adaptivefinitevolume".
```

This patch fixes the issue by installing them as `TARGETS`.

bump version to 2.7-git [ci skip]

See merge request !19

[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