Add toString() for WWC input data.

src/main/org/insa/algo/weakconnectivity/WeaklyConnectedComponentsData.java

@@ -13,4 +13,9 @@ public class WeaklyConnectedComponentsData extends AbstractInputData {
         super(graph);
     }
 
+    @Override
+    public String toString() {
+        return "Weakly-connected components from #0.";
+    }
+
 }