Bed model : wider & more simple

- Wider mattress : 75 cm (unrealistic, too narrow) -> 87.5 cm.
- Removed the nodeboxes planks under the bed : wasn't really necessary and it still looks good.
- Slightly tweaked an horizontal plank on the head part for use a common texture in this side.

![screenshot_147640949](https://cloud.githubusercontent.com/assets/7883281/4611587/bba4a88e-52bc-11e4-80ab-2a64c22ed5ac.png)
![screenshot_160285796](https://cloud.githubusercontent.com/assets/7883281/4613577/59bb50b2-52d7-11e4-82d6-52d886a8ebf4.png)