Mg center logo nav

![image](https://cloud.githubusercontent.com/assets/2095625/3552269/7eadefd8-08f4-11e4-9429-d20449e0e9f1.png)


![image](https://cloud.githubusercontent.com/assets/2095625/3552275/8f7b975c-08f4-11e4-9c78-92546701c95f.png)

Since the logo is centered in the `ul` I guess it'd be hard to move it out to the far left of the nav when in mobile view. Therefore it's duplicated. One in the `ul` that is hidden on small screens, and one that only shows up on small screens. Not pretty but I'd love to avoid js for this stuff!