Replace RefractionIndexItem with MaterialDataItem in GUI

Core/Export/ExportToPython.cpp

GUI/coregui/Models/GUIObjectBuilder.cpp

GUI/coregui/Models/ItemFactory.cpp

GUI/coregui/Models/MaterialDataItem.cpp

GUI/coregui/Models/MaterialDataItem.h

GUI/coregui/Models/MaterialItem.cpp

GUI/coregui/Models/MaterialItem.h

GUI/coregui/Models/MaterialModel.cpp

GUI/coregui/Models/MaterialModel.h

GUI/coregui/Models/item_constants.h

GUI/coregui/Views/MaterialEditor/MaterialUtils.cpp

GUI/coregui/Views/PropertyEditor/ComponentEditor.cpp

Tests/UnitTests/GUI/TestMaterialModel.h