Fix bug in index view of archived publications.

If an edition has sibling_in_progress set, but didn't actually have a
sibling in progress, this view would blow up.  This fixes that.
Add NI licence editions data
Tidy up output from importer
Merge remote-tracking branch 'origin/import-ni-licences'
Merge pull request #98 from alphagov/fix_archived_index_bug

Fix bug in index view of archived publications.