Adding GraphML output to options menu

src/main/java/Simulator.java

@@ -668,7 +668,7 @@ public class Simulator implements GraphModificationFunctions {
 
     private static Map<Integer, Integer> makeVertexToSequenceMap(Map<Integer, Integer> sequences, Integer startValue) {
         Map<Integer, Integer> map = new LinkedHashMap<>(); //LinkedHashMap to preserve order of entry
-        Integer index = startValue;
+        Integer index = startValue; //is this necessary? I don't think I use this.
         for (Integer k: sequences.keySet()) {
             map.put(index, k);
             index++;