Add remote entity support

We would like this module to support remote entities: https://www.drupal.org/project/remote_entity

Currently entity reference views widget will only work with entities that have a base table defined. Remote entities do not necessarily have this.

// Build entity tables.
  $entity_info = entity_get_info();
  foreach ($entity_info as $info) {
    if (isset($info['base table'])) {
      $tables[$info['base table']] = $info['entity keys']['id'];
    }
  }

The attached patch will add an additional foreach that will check if the entity controllers extend the RemoteEntityAPIDefaultController class. This is exactly how EFQ Views checks for remote entities.