Use the public Organisations API host (www.gov.uk)

We lost the ability to connect from CI to whitehall-admin, but we can happily
use the public URL to access it so let's do that.
Merge pull request #577 from rjc123/newsites

Config reporting.direct.gov.uk for turndown and transition to gov.uk
Merge pull request #578 from alphagov/use_public_organisations_api_url

Use the public Organisations API host (www.gov.uk)