Move colour bar out of breadcrumbs

When we have static pages in Spotlight, we'll want to include the colour
bar on pages where we don't have any breadcrumbs (eg the homepage).

This commit separates the two so they can be used independently.
Only display breadcrumb wrapper if crumbs exist
Move common configuration out of process_request

We'll need to reuse this configuration in all Spotlight pages, not
just pages that make use of process_request.
Add homepage

I've made a couple of changes while moving it across:

- Change link to blog and link text to be correct
- Remove live GOV.UK usage module (should be easy to re-add?)
- Add height and width to Transactions Explorer image, make it a link
Merge pull request #193 from alphagov/static-page-preparation

Add homepage