Add first stab at browse columns JavaScript

Load new data in via ajax and replace the contents of the page with it.
Use mustache to render the ajax responses

Use the shared mustache gem. Eventually this can share the templates
with Rails. But for the moment just use the templates on the client.
Highlight active link
Refactor section/subsction finders
Animate the moving of sections
Add push state for url changing
Set page title on new pages
Animate scrolling back to the top

On page change move back to the top so you can see the new content. Also
move the speed of all the animations into a variable so they can be
changed in one go rather than updating lots of numbers.
Don't act on click the page you are on

Also highlight hover links.
Sort results alphabetically
Don't highlight active link
Add jasmine rails for javascript testing
Add some tests for the browse columns

Also kick out if pushState isn't supported
Add detailed guides onto subsection pages
Configure asset host in development mode

When run under `govuk_setenv`, this configures the asset host to point
at the assets-origin on the dev VM. This will give us better dev-prod
parity, and enable running this behind the router in dev.
Only match two levels of browse
Prefix cache objects

So we can use the same cache for detailed and sections.
Remove logging
Mustache needs booleans
Handle back button navigation starting from root

If you start browsing from the root browse the back button should work
to get you back there.