SelectionProperty: rwSelected is a class method now

GUI/Model/Descriptor/SelectionProperty.h

GUI/Model/Device/BeamAngleItems.cpp

GUI/Model/Device/BeamItems.cpp

GUI/Model/Device/BeamWavelengthItem.cpp

GUI/Model/Device/InstrumentItems.cpp

GUI/Model/Device/RectangularDetectorItem.cpp

GUI/Model/Device/SpecularBeamInclinationItem.cpp

GUI/Model/Device/SphericalDetectorItem.cpp

GUI/Model/Sample/CompoundItem.cpp

GUI/Model/Sample/InterferenceItems.cpp

GUI/Model/Sample/MesocrystalItem.cpp

GUI/Model/Sample/ParticleItem.cpp

GUI/Model/Sample/ParticleLayoutItem.cpp