Adjusting .find_by_identity! to be forgiving

Instead of always relying on the URI, fallback on the
name_for_application_usage if the identity is not found.

@TODO - Answer why am I maintaining :identity and
  :name_for_application_usage?
Verifying that work objects can be reified

An object that is persisted to the database can be retrieved and will
be functionally the same as the original work object from memory.