New product comparison table added

This has been added, currently on /basic and /pro pages, as shown below.

Do we really want the links to also point to /basic and /pro, or somewhere else?

SVG's are accessible too!

![screen shot 2014-11-11 at 17 36 41](https://cloud.githubusercontent.com/assets/2903904/4997731/590c5cfc-69c9-11e4-9749-5b17d01d0d23.png)

@angusbayley just refactoring here - the darker grey background colour was originally only used on the Pricing page, but now also used in the comparison table too, so we gave that background colour it's own utility css class - called u-background-primary