Ref T189, context menu "Clear highlighting" only if there are highlighted rows

* added customMenu in template
* added hasHighlightedRows

src/blackgui/models/aircraftmodellistmodel.cpp

@@ -221,5 +221,9 @@ namespace BlackGui
             this->m_highlightStrings.clear();
             COrderableListModelDbObjects::clearHighlighting();
         }
+        bool CAircraftModelListModel::hasHighlightedRows() const
+        {
+            return !m_highlightStrings.isEmpty();
+        }
     } // namespace
 } // namespace

src/blackgui/models/aircraftmodellistmodel.h

@@ -71,9 +71,12 @@ namespace BlackGui
             //! The highlight color
             void setHighlightModelStringsColor(const QBrush &brush) { m_highlightColor = brush; }
 
-            //! \copydoc CListModelBase::clearHighlighting
+            //! \copydoc CListModelBaseNonTemplate::clearHighlighting
             virtual void clearHighlighting() override;
 
+            //! \copydoc CListModelBaseNonTemplate::hasHighlightedRows
+            virtual bool hasHighlightedRows() const override;
+
             //! Model strings
             QStringList getModelStrings(bool sort) const;
 

src/blackgui/models/listmodelbase.cpp

@@ -210,6 +210,12 @@ namespace BlackGui
             // can be overridden to delete highlighting
         }
 
+        bool CListModelBaseNonTemplate::hasHighlightedRows() const
+        {
+            return false;
+            // can be overridden to enable highlighting based operations
+        }
+
         void CListModelBaseNonTemplate::emitDataChanged(int startRowIndex, int endRowIndex)
         {
             BLACK_VERIFY_X(startRowIndex <= endRowIndex, Q_FUNC_INFO, "check rows");

src/blackgui/models/listmodelbase.h

@@ -114,6 +114,9 @@ namespace BlackGui
             //! Remove all highlighting
             virtual void clearHighlighting();
 
+            //! Has highlighted rows?
+            virtual bool hasHighlightedRows() const;
+
             //! Drop actions
             void setDropActions(Qt::DropActions dropActions) { this->m_dropActions = dropActions; }