Add insert order for overlayed widget to the side tab bar

- Set the default insert order to append

src/DockWidget.cpp

@@ -96,6 +96,7 @@ struct DockWidgetPrivate
 	CDockWidget::eMinimumSizeHintMode MinimumSizeHintMode = CDockWidget::MinimumSizeHintFromDockWidget;
 	WidgetFactory* Factory = nullptr;
 	double DefaultOverlayDockProportion = 0.25;
+	CDockWidget::eOverlayInsertOrder OverlayInsertOrder = CDockWidget::Last;
 	
 	/**
 	 * Private data constructor
@@ -1149,6 +1150,18 @@ double CDockWidget::DefaultOverlayDockProportion() const
 }
 
 
+//============================================================================
+void CDockWidget::setOverlayInsertOrder(eOverlayInsertOrder insertOrder)
+{
+	d->OverlayInsertOrder = insertOrder;
+}
+
+CDockWidget::eOverlayInsertOrder CDockWidget::overlayInsertOrder() const
+{
+	return d->OverlayInsertOrder;
+}
+
+
 //============================================================================
 void CDockWidget::raise()
 {