Setup responsive behaviour for CMS admin

Fairly simple responsive solution for tablets only. Container min-width set to 860px. 

Added JS for menu button alongside the button itself. There might be a better place to keep that.

**Screenshots**
![fuel_responsive_menu_closed](https://f.cloud.github.com/assets/630334/713866/e6f3d65e-dee1-11e2-9315-f81afd88c5b9.png)
![fuel_responsive_menu_open](https://f.cloud.github.com/assets/630334/713867/eb1204ae-dee1-11e2-92d8-7e8b2a0caef4.png)