Bring changes from Pombola back into master

This and https://github.com/mysociety/pombola/pull/1079 should bring pombola and sayit back in sync again.

NB: https://github.com/mysociety/pombola/issues/1027 has another 2 tasks to ensure all is tickety-boo.  (Refactor breadcrumbs some more, to avoid pombola whole-template override; check za-hansard importer works without duplicate slug errors.)