Adding scope attribute each for subject, attribute_type, relation_type, object_value and right_subject fields


- Files modified:

  1) models.py

     - Fields added in GAttribute class: subject_scope, attribute_type_scope, object_value_scope
     - Fields added in GRelation class: subject_scope, relation_type_scope, right_subject_scope

  2) add_fields_to_existing_documents

- Please run following command: ```python manage.py add_fields_to_existing_documents```