Remove 'get' from IMaterial methods

Core/DecoratedFormFactor/FormFactorDecoratorMaterial.cpp

Core/Export/ExportToPython.cpp

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/Layer.cpp

Core/Multilayer/SpecularMagnetic.cpp

Core/Multilayer/SpecularMatrix.cpp

Core/Particle/Particle.cpp

GUI/coregui/Models/GUIObjectBuilder.cpp

Tests/UnitTests/Core/Other/HomogeneousMagneticMaterialTest.h

Tests/UnitTests/Core/Other/HomogeneousMaterialTest.h

auto/Wrap/doxygen_core.i

auto/Wrap/libBornAgainCore.py

auto/Wrap/libBornAgainCore_wrap.cpp