back to use friendly id for setting the slug
added history to friendly id
get the slug from friendly id
handle decision not found
added migration script to keep the history of slugs, and the friendly_id initialisers
Merge branch 'develop' into feature/slug_refactor
removed old code
Merge pull request #143 from ministryofjustice/feature/slug_refactor

Back to use friendly_id for the slug, with history