Live summary

The last live summary changes (still behind a switch).

- [New] Summary is pulled from the back end, and then automatically refreshed if a new one is rendered after an auto update
- [New] New `.from-content-api--small` class for smaller text. Used here in the right column for the summary text.
- [Changed] Article breakpoints are in _vars.scss (to be usable in any other module)

Todo before switching this feature on:
- design review & changes
- integration tests
- editorial review 
- SEO review

![summary-iphone](https://f.cloud.github.com/assets/85783/1115919/a44bea44-1a32-11e3-81dd-a9433fce2569.gif)

![summary-ipad](https://f.cloud.github.com/assets/85783/1115920/a7bf329e-1a32-11e3-87d8-845023602988.gif)