Shifted the canvas to the back of the window when updated.

This is to preserve the way the boats are still shown on the front when the course i reloaded.
As the main live stream has been down, this still needs to be tested.

src/main/java/seng302/controllers/CanvasController.java

@@ -250,6 +250,7 @@ public class CanvasController {
             gc.fillRect(0,0, CANVAS_WIDTH, CANVAS_HEIGHT);
             gc.restore();
             addRaceBorder();
+            canvas.toBack();
         }
     }