Bugfix in RefractiveIndexItem with screwed variant type.

GUI/coregui/Models/LayerRoughnessItems.cpp

GUI/coregui/Models/MaterialItem.cpp

GUI/coregui/Models/MaterialModel.cpp

GUI/coregui/Models/MultiLayerItem.cpp

GUI/coregui/Models/ParameterizedItem.cpp

GUI/coregui/Models/RefractiveIndexItem.cpp

GUI/coregui/Models/RefractiveIndexItem.h

GUI/coregui/Models/ScientificDoubleProperty.h

GUI/coregui/Models/SessionModel.cpp

...ews/Components/MaterialEditor/MaterialPropertyBrowser.cpp

...Views/Components/MaterialEditor/MaterialPropertyBrowser.h

...coregui/Views/Components/MaterialEditor/MaterialUtils.cpp

.../Views/Components/SampleDesigner/SamplePropertyEditor.cpp

GUI/coregui/mainwindow/mainwindow.cpp

GUI/coregui/utils/GUIHelpers.cpp

GUI/coregui/utils/GUIHelpers.h