Fix some duplication in local interactions

Because the importer ran on multiple servers simultaneously, we've ended up with some duplicate local interactions in the database.  This includes a migration to clean them up.

It also pulls in content_models with an added validation to help prevent this occurring again.  Once the data is cleared up, we can add a db level constraint to back this up.

This change also relaxes a SNAC validation in the importer so that NI SNACs will work.