Moved polarization check to DWBASimulation and added a matrix-valued output data structure there to hold polarized scattering data

- 3rd person form: "Does" this or that.
- For all const methods that return something: "Returns" ...
- For boolean return value: "Returns true if " ...

manual editing of @brief ("defines ...", "implements ..."), removed multiple white lines

Rewritten IsGISAXS Example 3 code using the new Experiment class (2): added MultiLayerDWBASimulation class.

Refactored decorator classes, added Experiment, Beam and Detector classes and added prototype pattern to many classes (clone() function)