Added required interfaces and preliminary implementation for magnetic calculations in IInterferenceFunctionStrategy classes and DecoratedLayerDWBASimulation

- 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

Moved implementation of Hann function to strategy class and implemented the scattering intensity calculation