Add GDS as organisation to all directgov and businesslink sites
Add a rake task to validate that hosts appear only once

A host should never appear on multiple sites at once. We want to be
able to reassign hosts to other sites in Transition's orgs_sites_hosts
import, and this task makes that a little safer. The task is included
in the CI build so that we can see clearly if any duplicate hosts are
present across all site yaml files.
Merge pull request #736 from rjc123/newmappings

Add GDS as organisation to all directgov and businesslink sites
Merge pull request #737 from alphagov/validate_hosts_unique

Add a rake task to validate that hosts appear only once
New date for DCLG LF
Merge pull request #738 from rjc123/newmappings

New date for DCLG LF
Add Military Aviation Authority to transition tool
Merge pull request #739 from rjc123/newmappings

Add Military Aviation Authority to transition tool
Add query string and extra org for site
Date changes for mod sites
Add relevant query strings determined from arcl
Merge pull request #740 from rjc123/newmappings

Query strings and date changes for upcoming sites
Configure nationalcollege.org.uk on the transition tool
Configure MHRA on transition tool
Merge pull request #742 from rjc123/zendesk

Configure MHRA on transition tool
add extra org for ODI
Confirm go-live date for ODI
Confirm go-live date for SSAC
Confirm go-live date for IIAC
Update the timestamp for defra_cpet