Make browse links alphabetical on homepage

So that they match the order of the new browse pages and give people a
little more context as to what they are looking at when they navigate
through.

Done as three lists which is less than ideal but due to the limitations
of CSS floats I can't think of any better ways to achieve this.
Make blue top span full page in IE <= 7

There is an overide setting the main width for content pages, however we
don't want or need that width on the homepage as we manually set the
widths. Force the width to be auto on the homepage.
Merge pull request #644 from alphagov/sort-homepage-links

Make browse links alphabetical on homepage

https://www.pivotaltracker.com/story/show/74209294