Add rake task to register Contacts with router

Hard coding HMRC for now. Relates to
https://www.pivotaltracker.com/s/projects/1010882/stories/67458078
Merge pull request #98 from alphagov/add-router-registration-rake-task

Add rake task to register Contacts with router
Merge commit '892d497ed282cd1d0a84a6d9eafeae9af3ced42a' into HEAD