Redesigned /paying-through-gocardless

![paying through gc preview](https://cloud.githubusercontent.com/assets/883598/3700439/9d46a420-13e0-11e4-827c-db0d57af2433.png)

Would be nice to abstract the icons we use. Something like `content-icon--settings-primary-large` 
Naming: `content-icons__[icon-name]-[color]-[size]`
Colours: primary, secondary, accent
Hopefully we can fit most of our icons in that structure?