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/1514/5206298/ed0424e2-7597-11e4-8a94-315f2719f7d7.png)