Style pages to look like GOV.UK

Use Slimmer (and hence Static) to add the GOV.UK header and footer to our
pages.

Also use the title govuk_component to render the h1 in the GOV.UK style.
Disable the global breadcrumbs

This was adding a link to "Home" which seems a bit out of place when there
isn't any hierarchy.
Fix the indentation of the page title

There are styles in Static which do this for us, but they depend on the h1
being inside a header element with the page-header class.