Access policy (Public/Private) updated - Private part now works in list-view


**Functionalities implemented:**

1) **Bug resolved: Access policy (Public/Private) updated - Private part now works in list-view**

   - If you set a node's Privacy as private (in edit mode), then it will be visible only to you in the list-view; and others won't be able to see the node even if the group is public.
   
2) **List-view's search is also modified accordingly**

NOTE: In order to achieve above functionality, find query is modified.

```
collection.Node.find( ...,
                      ...,
                      '$or': [
                               {'access_policy': u"PUBLIC"},
                               {'$and': [
                                 {'access_policy': u"PRIVATE"}, 
                                 {'created_by': request.user.id}
                                 ]
                               }
                             ]
)
```