Refactor FE routes to remove confusing scoping.

This was overly complicated for what boiled down to basically 2 get
routes and a couple of redirects.
Support new contacts URLs

Contact pages are going to be served from
/government/organisations/<org_slug>/contact instead of the original url
of /contact/<org_slug>. This change makes this app support both schemes.
The old one will be removed once everything has switched over.
Merge pull request #143 from alphagov/update_frontend_urls

Support new contacts URLs