Fix for #12 in simonstrator-api (fix BasicGraph#createNode)

src/de/tudarmstadt/maki/simonstrator/api/common/graph/BasicGraph.java

@@ -152,9 +152,7 @@ public class BasicGraph implements Graph {
 		if (this.containsNode(id)) {
 			return this.getNode(id);
 		} else {
-			Node newNode = new Node(id);
-			this.addNode(newNode);
-			return newNode;
+			return new Node(id);
 		}
 	}