Topic detail view as list of available contents in topic according to its mime type 

Topic landing page has been changed as not concept graph but the resource contents in that topic, so that user can easily recognize and navigates through available resources for that topic.

Contents in topic displayed as a topic detailed view. Topic's landing page now consists of lists of resource contents for that topic differentiated according to mime type. 
```get_content()```  --> method returns the dict with name and resource ID's, resource contents differentiates according to its mime type.