Centering the ingot texture

Problem :
This is not obvious, but ingotPile are oddly textured. 

The mapping is different for each layer. 
lvl1, lvl3, lvl5, lvl7 ---------------------------- lvl2, lvl4, lvl6, lvl8
![lvl1](https://cloud.githubusercontent.com/assets/401965/4927821/d5109be0-653e-11e4-8e0c-50adebcab591.png) ![lvl2](https://cloud.githubusercontent.com/assets/401965/4927823/d6c364c2-653e-11e4-8884-b55af7ffce78.png)

Therefore, it is difficult to adapt the texture for have effect on the ingots. 

---
One solution :

provided with this pull request :

One mapping for all.
![lvl1 2](https://cloud.githubusercontent.com/assets/401965/4928009/86d73cde-6540-11e4-8895-1c59dd01fe5e.png)

Avantage :
- One mapping for all ingots.
- Snap to pixel grid.
- Pixel (almost) square when rendering.
- Free edge.