nodeview: added 'add' button to toolbar

app/widget/nodeview/nodeviewtoolbar.h

@@ -19,6 +19,8 @@ public slots:
   }
 
 signals:
+  void AddNodeClicked();
+
   void MiniMapEnabledToggled(bool e);
 
 protected:
@@ -29,6 +31,8 @@ private:
 
   void UpdateIcons();
 
+  QPushButton *add_node_btn_;
+
   QPushButton *minimap_btn_;
 
 };