Data migration to fix some untyped publications

Several published publications do not have a valid publication type.
This data migration sets their type based on information provided by
departments, defaulting to 'Guidance' where a type has not been
provided.
Merge pull request #649 from alphagov/fix-publication-types

Data migration to fix some untyped publications

https://www.pivotaltracker.com/story/show/52988963