Add ONS and statistics.gov.uk as new sites
Merge pull request #817 from rjc123/newmappings

Add ONS and statistics.gov.uk as new sites
Change the transition date of the DCLG Planning Portal site to December
Change the transition date of the Government Chemist to July 31st
Merge pull request #819 from alphagov/change_date_of_government_chemist

Change the transition date of the Government Chemist to July 31st
Merge pull request #818 from alphagov/change_date_of_dclg_planning_portal

Change the transition date of the DCLG Planning Portal site to December
Separate DTI to own archive site
Add ONS and statistics.gov.uk as new sites
Configure mod_ssmt on transition tool