Update wrought iron fences

- Add nodeboxes (cross, and crosses + sides for the corner piece).
- Readjustment of the selection boxes.

![screenshot_595343538](https://cloud.githubusercontent.com/assets/7883281/4689820/95a6f5d2-56cd-11e4-9877-5f32b978526f.png)
![screenshot_595373654](https://cloud.githubusercontent.com/assets/7883281/4689821/982ec78a-56cd-11e4-9829-572c5772c22c.png)