Script updated for fetching pandora videos

*  ```fetch_wetube_video.py```  --> script updated to fetch pandora videos from wetube.
   *  ```member_of``` field updated in script --> included "File" ST along with "Pandora_video" ST
   *  ```created_by, modified_by & contributors``` fields updated with "nroer_team"  user id 

* ```sync_existing_documents``` --> Script updated for already created pandora videos to set "created_by", "modified_by" , "contributors"  and "member_of" field.