Responsive viewer

Moved to facia app, because of SSL issues with having it in facia-tool. Specify a target page with the url hash, e.g. `/responsive-viewer#http://www.theguardian.com/uk`

Also needs: https://github.com/guardian/platform/pull/248

![fronts-tool](https://f.cloud.github.com/assets/1147913/1327453/7131432a-34ef-11e3-92bf-370f35e03b74.png)