NIF: added NiStencilProperty record handling

NiStencilProperty appears in Better Clothes plugin. If it not handled,
some parts of NPCs bodies will be not rendered.

Balmora, square near House Hlaalu quarters:
![bc_before](https://f.cloud.github.com/assets/1856842/202573/2a3ae7fa-8117-11e2-9269-a35c954790a0.png)
![bc_after](https://f.cloud.github.com/assets/1856842/202574/2eb9b70c-8117-11e2-9047-70bcfd0b526f.png)