Class view: Fix expanding of items on double click

Task-number: QTCREATORBUG-2536
Change-Id: I94471c265c9f9dbffe253d7c6e8a1e834b47f91f
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@theqtcompany.com>

src/plugins/classview/classviewnavigationwidget.h

@@ -72,6 +72,7 @@ signals:
 
 public slots:
     void onItemActivated(const QModelIndex &index);
+    void onItemDoubleClicked(const QModelIndex &index);
 
     void onDataUpdate(QSharedPointer<QStandardItem> result);