Sublink kickers

Adds optional kickers to sublinks:
![fronts-tool](https://cloud.githubusercontent.com/assets/1147913/4012529/a0333c36-2a0e-11e4-9924-0eee2c262bfa.png)

These kickers are selectable in the tool:
* analysis
* background
* breaking-news
* detail
* in-depth
* reaction

Think he did here ... https://github.com/guardian/frontend/commit/55fe28ba0262cb656c36d53bf1782468ec75ed0b