Update methods for performing record metadata updates

* per default, try the more modern approach of updating the draft that
  is associated with the record's recid (service.update_draft() followed
  by service.publish()), and only in case of error fall back to
  service.update()
* add a "direct" variant of updating metadata, which circumvents the
  record service and directly modifies the record's metadata
* this is not recommended, but can come in handy when more direct access
  is required than the record service allows