(Towards macroscopically varying microstructure) Switch to Microstructure - PythonClasses for Material/Problem-Setup

For a macroscopically varying microstructure we need to be able to have (local) indicator-functions (and maybe other parameters, prestrain etc.) for the micro/cell-problem that depend on the macroscopic material point. Currently, all the parameters are read from a Python-Input-File and the indicator-functions are cast to Dune::LocalFunctions.

We move to a Python-Class-based definition and define a 'class Microstructure' in the Python-Input-File that stores all the microstructure information and carries a 'macroPoint' member variable that allows to control the indicator-functions etc. depending on the macroscopic material point.