Replace IMaterial class hierarchy by single HomogeneousMaterial

Core/Computation/Slice.h

Core/DecoratedFormFactor/FormFactorDecoratorMaterial.cpp

Core/DecoratedFormFactor/FormFactorDecoratorMaterial.h

Core/DecoratedFormFactor/IFormFactorDecorator.h

Core/Export/ExportToPython.cpp

Core/Export/SampleLabelHandler.cpp

Core/Export/SampleLabelHandler.h

Core/Material/HomogeneousMagneticMaterial.cpp

Core/Material/HomogeneousMagneticMaterial.h

Core/Material/HomogeneousMaterial.cpp

Core/Material/HomogeneousMaterial.h

Core/Material/IMaterial.cpp

Core/Material/IMaterial.h

Core/Multilayer/FormFactorDWBA.h

Core/Multilayer/FormFactorDWBAPol.h

Core/Multilayer/Layer.cpp

Core/Multilayer/Layer.h

Core/Multilayer/LayoutStrategyBuilder.cpp

Core/Multilayer/LayoutStrategyBuilder.h

Core/Multilayer/MultiLayer.cpp