Update consultation dates to match style guide

https://www.pivotaltracker.com/story/show/60518508
Handle empty groups when reording doc collections

The document_ids parameter isn't sent with the request if one of the
document collection groups is empty. This change handles that
gracefully.
Merge pull request #1074 from alphagov/update-consultation-dates

Update consultation dates to match style guide

https://www.pivotaltracker.com/story/show/60518508
Merge pull request #1077 from alphagov/fix-document-collection-reordering-empty-group-500-error

Handle empty groups when reording doc collections

https://www.pivotaltracker.com/story/show/61211960