Preparation work for onwards journeys


- Feature switch
- Prepare the DOM for inline article upgrades
- Add the body content to the trails model

Ie, it lets you do this sort of thing in any trail block ...

![package](https://f.cloud.github.com/assets/84996/949172/29506c6e-0378-11e3-8a31-b85e5c838660.png)

@phamann I think this is better than doing even more XHR. Thoughts?