Change description of status to public/unavailable
Change description of status to public/unavailable

In discussion with @cathrooney we’ve decided that the statuses should be:
- ‘unavailable’ if either an admin or a supplier has removed/unpublished/turned
  off a service
- ‘public’ if the service has been published/made available/turned on

alphagov/digitalmarketplace-admin-frontend,alphagov/digitalmarketplace-admin-frontend,alphagov/digitalmarketplace-admin-frontend,alphagov/digitalmarketplace-admin-frontend