New ItemStackPresenter for uniform treating of SessionItem's stacked widgets.

GUI/coregui/CMakeLists.txt

GUI/coregui/Models/ApplicationModels.cpp

GUI/coregui/Models/ItemFactory.cpp

GUI/coregui/Models/RealDataItem.cpp

GUI/coregui/Models/RealDataItem.h

GUI/coregui/Models/item_constants.h

GUI/coregui/Views/CommonWidgets/ItemSelectorWidget.cpp

GUI/coregui/Views/CommonWidgets/ItemSelectorWidget.h

GUI/coregui/Views/CommonWidgets/ItemStackPresenter.h

GUI/coregui/Views/CommonWidgets/ItemStackWidget.cpp

GUI/coregui/Views/CommonWidgets/ItemStackWidget.h

GUI/coregui/Views/ImportDataView.cpp

GUI/coregui/Views/ImportDataView.h

GUI/coregui/Views/ImportDataWidgets/RealDataEditorWidget.cpp

GUI/coregui/Views/ImportDataWidgets/RealDataEditorWidget.h

GUI/coregui/Views/SessionModelView.cpp