Added implementation for FormFactorPol and used this for polarized Born Approximation in LayerStrategyBuilder

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

Implemented cloneInvertB() on ISample classes and use a MultiLayer with inverted magnetic field for the outgoing scattering states if necessary; refactored MagneticCoefficientsMap

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