Bugs removal regarding group_set migration


Files modified:

1) migrate_group_set.py
   - Bug resolved: Now also updating user-groups & Files(Images/Videos) group_set field.
   
2) group.py
   - Bug resolved: Displaying group information
   - group_dashboard() modified: 'node' variable added to context variable

3) file.py
   - Error resolved: img_type parameter added to save_file() function's parameter-list.
   
4) ndf_tags.py
   - Bug resolved: Url-redirection regarding private groups.