changed to string (should be a bit faster now)

src/main/java/it/unibz/inf/isochrone/network/NodeConnection.java

@@ -112,7 +112,7 @@ public class NodeConnection {
 
 	@Override
 	public String toString() {
-		return "NodeConnection [sourceNode=" + sourceNode + "]";
+		return "NodeConnection [sourceNode(id)=" + sourceNode.getId() + "]";
 	}
 
 	// Private static methods