Now we can make a collection of resources for topic

By considering topic is a node(leaf node), we can make a collection of resources in it.
Changes made as follows: 
* ``` topic_create_edit.html ```  -->  Added the collection tab for topic to make a collection of resources

* ``` ajax_views.py ```  -->  Condition applied for creating theme topic hierarchy so that topic should remain as leaf node, no branches should be created for topic while making a collection of resources in it.

* ``` browse_topic.py ```  -->  Bug resolved in maintaning the uniqueness for root level themes

* ``` methods.py ```  -->  For topic now we can maintain the collection of resources, query added to fetch the collection drawer for topic

* ``` theme.html ```  -->  Currently disabled the translate feature for themes