Add a variant in the inline link card test

As per @commuterjoy request, we now have 3 variants in the inline link card test:
- control (no cards)
- link-card (internal links get cardified)
- link-card-all-origins (links to whitelisted domains get cardified)

Related: #1466 #1342.

We need to adapt [the hypothesis](https://github.com/guardian/frontend/blob/master/docs/experiments/linked-content-cards-sidebar.md): place your bets!

### A yummy example:

Thanks Matt for pointing to this great card (in /lifeandstyle/2010/feb/06/experience-bubonic-plague): 

![screen shot 2013-09-09 at 15 52 30](https://f.cloud.github.com/assets/85783/1107551/816bb442-195f-11e3-8292-f14efd8dcd09.PNG)


![ ](http://s1.developerslife.ru/public/images/gifs/284c24e2-9fdd-45e6-be57-3f4f1f458cc7.gif)