Add TranslateZ hack 

By adding the translateZ hack to Bootstrap .navbar, performance increases dramatically for example take the following results from Chrome Dev Tools:
![screen shot 2013-10-08 at 10 06 43 pm](https://f.cloud.github.com/assets/1643741/1294884/b2e17104-3095-11e3-8166-3b4a5025bbd7.png)
![screen shot 2013-10-08 at 10 07 00 pm](https://f.cloud.github.com/assets/1643741/1294885/b7a34f14-3095-11e3-96da-d1e500596415.png)