Added necessary required fields to GTriple, GAttribute, and GRelation classes


Files modified:

1) models.py:
   * Following required fields added to GTriple:
     - name
     - subject
     
   * Following required fields added to GAttribute:
     - attribute_type
     - object_value
     
   * Following required fields added to GRelation:
     - relation_type
     - right_subject