Merge branch 'reducedSessionModelView' into 'develop'

GUI/View/Common/ItemSelectorWidget.cpp

GUI/View/Common/ItemSelectorWidget.h

GUI/View/Common/ModelTreeView.cpp

GUI/View/Common/ModelTreeView.h

GUI/View/Fit/FitParameterDelegate.cpp

GUI/View/Fit/FitParameterDelegate.h

GUI/View/Fit/FitParameterWidget.cpp

GUI/View/Fit/FitParameterWidget.h

GUI/View/PropertyEditor/CustomEditors.cpp

GUI/View/PropertyEditor/CustomEditors.h

GUI/View/PropertyEditor/MultiComboPropertyEditor.cpp

GUI/View/PropertyEditor/MultiComboPropertyEditor.h

GUI/View/PropertyEditor/PropertyEditorFactory.cpp

GUI/View/Toplevel/SessionModelView.cpp

GUI/View/Toplevel/SessionModelView.h