Code cleanup in FancyGroupProperty

GUI/coregui/Models/FancyGroupProperty.cpp

GUI/coregui/Models/FancyGroupProperty.h

GUI/coregui/Models/GroupPropertyRegistry.cpp

GUI/coregui/Models/GroupPropertyRegistry.h

GUI/coregui/Models/ParameterizedItem.cpp

GUI/coregui/Models/SessionModel.cpp

...ews/Components/InstrumentWidgets/DetectorEditorWidget.cpp

GUI/coregui/Views/Components/SampleDesigner/ParticleView.cpp

.../Views/Components/SampleDesigner/PropertyBrowserUtils.cpp

...ui/Views/Components/SampleDesigner/PropertyBrowserUtils.h

...iews/Components/SampleDesigner/PropertyVariantFactory.cpp

.../Views/Components/SampleDesigner/PropertyVariantFactory.h

...iews/Components/SampleDesigner/PropertyVariantManager.cpp

.../Views/Components/SampleDesigner/PropertyVariantManager.h

Tests/UnitTests/TestGUI/TestParaCrystalItems.h