Move edition state filtering into filterer

This is a better place for it as it means the sanitisation is always
performed rather than just when the Admin::EditionFilter is
used in Admin::EditionsController.
Document linker returns pre-publication editions

You should never have to link an announcement to a published edition
as there would be no point in announcing it if it's already been
published!
Adjust search indexing for StatisticsAnnouncement

This relies on the new "metadata" property added to the rummager
schema.