Services Modules migration improvements

Improves on #594 migrations by refusing to run if the user has missing module destinations for services data which would result in data loss. If the user doesn't care about that data they should, preferably, install that module for the migration and then migrate zero on that module before removing it from INSTALLED_APPS. Alternatively they could wipe that columns data in SQL before running the migration again.

Also allows users to specify SERVICES_MIGRATED=True to prevent migrations complaining about the order of migrations when enabling a service which was not migrated before the services migration. The 0013 migration will drop all services module migration dependencies if SERVICES_MIGRATED is set to True.