Article sponsorship

- Sponsorship message based on Content API tone tag.
- The ad server is then used to target an advert at the sponsor based on the URL.
- The sponsorship message links to www.theguardian.com/sponsored-content

![carphone-warehouse](https://f.cloud.github.com/assets/84996/1861346/06563942-77c1-11e3-9b39-32b5b13b84ac.png)

/cc @kenlim @paulrobertlloyd First cut - thoughts?