Copy across the edition_policy_groups on policies

https://www.pivotaltracker.com/story/show/46527781
Data migration to create new EditionPolicyGroups

These are for the EditionPolicyGroups that were orphaned becase the
relations were not being copied on draft.

This goes through and updated all old editions that are missing the
policy groups
Merge pull request #409 from alphagov/policy-copy-edition-policy-groups

Copy across the edition_policy_groups on policies

https://www.pivotaltracker.com/story/show/46527781