Minor bug fixes - Edit button for group-node; Merge & revert buttons; groups drop-down list

**Functionalities implemented:**

1) Bug fixed: **Edit button for group-node listed only to either owner of the node or superuser**

   - File modified:
   
     1) ```templates/ndf/node_ajax_view.html``` - Additional if block put up

2) Bug fixed: **Merge & Revert buttons listed only to either owner of the node or superuser**

   - File modified:
   
     1) ```templates/ndf/version_page.html``` - Additional if block put up  

3) Bug fixed: **User-group included in drop-down list, even if list exceeds maximum count of nodes (i.e. 10)**

   - File modified:
   
     1) ```templatetags/ndf_tags.html```
         - get_user_group() - Query modified (Replaced no.of nodes count i.e., 10 with 9)