Implement reader for dune-grid vtu files

See merge request extensions/dune-vtk!8

Use mapDatTypes for associating enum to type for header integer types and DataArray types

Extend the mapDataTypes function to support constraints on the types

See merge request extensions/dune-vtk!13

add mapping for Vtk::DataTypes to real types

See merge request extensions/dune-vtk!10

Store IDs of DataArrays using section name and Name attribute

See merge request extensions/dune-vtk!6

Correct typo in afor[e]going

See merge request extensions/dune-vtk!7

Add missing dune-localfunctions dependency into dune.module file

See merge request extensions/dune-vtk!5

reduce module dependencies

See merge request extensions/dune-vtk!3

replace explicit url in gitlab-ci.yml by internal includes

See merge request extensions/dune-vtk!4

Added data reader to VtkReader and a grid-function representation of the read data

See merge request iwr/dune-vtk!24

remove the central forward declaration

See merge request spraetor/dune-vtk!32

Error handling

See merge request spraetor/dune-vtk!31

remove some unused_variable and integer comparison warnings

See merge request spraetor/dune-vtk!30

make an explicit cast to field type for shape-function values

See merge request spraetor/dune-vtk!29

make an explicit cast to field type for shape-function values to allow float128 ctype grids. Note: the problem is that the runtime-order lagrange finite-elements do not support different range-type than double internally.

Refactoring/namespace changes

See merge request spraetor/dune-vtk!28