Turn primary footer blue

Incorporates updated `guss-colours` and attendant updates to the header.

![screen shot 2014-08-07 at 17 07 38](https://cloud.githubusercontent.com/assets/867233/3844893/2814db32-1e4d-11e4-8b34-5c85b0da35b4.png)

is now

![screen shot 2014-08-07 at 17 08 00](https://cloud.githubusercontent.com/assets/867233/3844902/33cd64a8-1e4d-11e4-9b9a-fced3c1e1b3d.png)


`.l-footer-primary` spans the full width and has the sidebar colour for its background