Bug resolved: Now empty (including only spaces) tag-values were not getting saved

**Functionalities Implemented**

* Bug resolved: Now empty (including only spaces) tag-values were not getting saved
  - Files changed:
    ```
    views/methods.py
    ```

* Shelf icon is visible only if user is logged-in.
  - Files changed:
    ```
    templates/ndf/node_ajax_view.html
    ```