Responsive version of /paying-through-gocardless

![responsive-preview](https://cloud.githubusercontent.com/assets/883598/3903817/e5f0a55a-22d0-11e4-8beb-e445f277a04e.jpg)

Includes a number of utilities that represent the beginning of a framework for building responsive splash pages. Pull down and test in the browser & mobile!
Would be nice to apply site wide, maybe try setting initial-scale?