Feature/add dune vtk bindings

See merge request extensions/dune-vtk!11

[bugfix]

[bugfix]

[to be dropped] added a test using some dune-fem bindings to test different aspects of the VtkWriter bindings

use 'pointData' instead of 'pointVector' as argument for vtkWriter since
that argument can also be used for tensors.

[python] remove dune packages from 'install_requires' in setup.py.in

add metadata to dune.module for pip packaging

add cellData method and add missing parameter to constructor of write

remove test requiring dune-fem (moved to dune-fem)

fix cut and paste error in dune.module file

minor change to test

export the first vtk writer (unstructured vtk) still very crude

improve testvtk.py script

[bugfix] added missing 'unkown' to 'DataTypes' to_string

added lists for enum to allow for iteration which help with the export topython

Remove 'Dune::void_t' in favor of simple concept check

See merge request extensions/dune-vtk!26

make grid functions default constructible

See merge request extensions/dune-vtk!21

Fix integer comparison and missing install file warnings

See merge request extensions/dune-vtk!23

fix integer comparison warning

See merge request extensions/dune-vtk!22

replace is_indexable by IsIndexable

See merge request extensions/dune-vtk!20

Use the dune-core docker images as base for the tests

See merge request extensions/dune-vtk!18

Remove CI_TOOLCHAIN variable from gitlabci

remove manual installation of dune-uggrid

remove dune-typetree and dune-functions from installation list

drop support for dune-2.6

Remove VTK::Precision for dune-grid < 2.7

See merge request extensions/dune-vtk!19

Remove semicolon after if condition

See merge request extensions/dune-vtk!17

Make the Vtk::Function overloads more robust and set better default values

See merge request extensions/dune-vtk!16

Export some types and data

See merge request extensions/dune-vtk!14

Cleanup of Function and LocalFunction interface

See merge request extensions/dune-vtk!12

Use RangeTypes to determine name of first Scalars, Vectors, or Tensors DataArray

add AUTO RangeType

Add setFieldInfo member

Cleanup of Function and LocalFunction interface, add setter and getter and make LocalFunction evaluate method avare of numComponents

flexible header type

See merge request extensions/dune-vtk!9

Add method to set compressor type