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* This is necessary in order to keep all the parameters available through the method parameters() when cloning. In particular the clone() method of PowerLaw class was creating a deep copy of the Peclet class different to the one accessible via the Transport interface class.

* The reason for this change is that although dune-grid has its own conversion to a bindable functions it chooses a wrong VTKInfo for tensors. With this change, we select the correct VTKInfo.

* On release 2.6, dune-grid will throw an exception due to a wrong setup of the VTKInfo. So this will fail right now.
* A way to solve this would be to create a simple writer and add data together with the correct VTKInfo.

* With inline function we avoid duplicated references to the function

Merge branch 'master' into 142-add-parameterization-for-the-effective-hydrodynamic-dispersion-tensor

Implement new VTK file reader

See merge request !143

Update installation instructions for Ubuntu.
`pip install vtk` suffices for macOS.

[skip ci]

[skip ci]

* Install package `python3-vtk7`.
* Disable command line prompts while installing packages.
* Do not install recommended packages.

* Install python3-vtk7 non-interactively.
* Install libxt-dev to see if this suffices.