We forgot to add these changes to pull requests which were in
development before we upgraded to Rails 5.
We're also moving the rubocop rules to the basic files, so we're
notified when we inherit from `ActiveRecord::Base`.
- Add :date_of_birth and :postal_code to Signature to allow send these
fields to CustomCensusAPI
- Add new model presence validates: Only validate :date_of_birth and
:postal_code presence when the application has configured Remote Census
and their alias fields has values.