Register the browse routes with the router

This adds a new Rake task to register the '/browse' and '/browse.json'
routes to the collections app. 

At the present time, we do not want this to run automatically, so this 
remains a standalone Rake task that must be run manually in the preview
environment.
Unregister the existing browse redirect routes

At present `/browse/business` and `/browse/visas-immigration` redirect 
to their special-case counterparts. This is going away, and we'll be 
removing these routes from router-data soon. 

Until then, we need to ensure that these aren't registered whenever we 
register the mainstream browse routes.