Add isDraw() method to ChessEngine

schach/src/main/java/de/hs_mannheim/informatik/chess/model/ChessEngine.java

@@ -78,4 +78,9 @@ public class ChessEngine {
     public boolean isStalemate() {
         return board.isStaleMate();
     }
+    
+    public boolean isDraw() {
+        return board.isDraw();
+    }
+    
 }