added constructor to allow variant subtyping

Sorting/QuickSorter.java

@@ -6,6 +6,10 @@ public class QuickSorter extends Sorter{
         super("quick", filename);
     }
 
+    public QuickSorter(String qsortVariant, String filename){
+        super(qsortVariant, filename);
+    }
+
     void sort(){
         quickSort(0,numbers.length-1);
     }