ui: Added show definition context menu action for graph nodes (issue #83)

* use 'show definition' context menu action or 'Ctrl/Cmd + Left Click' to show definition of node in code

src/lib_gui/qt/graphics/QtGraphicsView.h

@@ -57,6 +57,7 @@ private slots:
 
 	void exportGraph();
 	void copyNodeName();
+	void showDefinition();
 	void hideNode();
 	void hideEdge();
 	void bookmarkNode();
@@ -94,6 +95,7 @@ private:
 
 	QAction* m_exportGraphAction;
 	QAction* m_copyNodeNameAction;
+	QAction* m_showDefinitionAction;
 	QAction* m_hideNodeAction;
 	QAction* m_hideEdgeAction;
 	QAction* m_bookmarkNodeAction;