Added "location" field to Node class for geo-tags


* Files modified:
  + models.py: 
    - Field added into Node class with following specifications:-
    1) name: location
    2) data-type: dict

* Files added:
  + ".../ndf/management/commands/add_fields_to_existing_documents.py" - Consists of code for following:
    - code of "add_policy.py" file: adding "access_policy" field to existing documents 
    - adding "location" field to existing documents 
    
* Files deleted (Removed unnecessary files as those were not required anymore!):
  - ".../ndf/urls.py"
  - ".../ndf/management/commands/add_policy.py"