Mock up the Sign Out interstitial in the style-guide (bug 1103072)


![styleguide](https://cloud.githubusercontent.com/assets/1514/5205886/29802a42-7593-11e4-9177-79aa776af5a3.png)


![styleguide](https://cloud.githubusercontent.com/assets/1514/5205879/1fe8037e-7593-11e4-8f9e-a1493c7501f1.png)