Document display view modified

Now document display view in files is modified.
Also you can now edit and make collections of documents.
Implemented : 
```
document_detail.html   --> Inherited details view template for documents display view
document_edit.html   -->  Inherited edit view template for documents edit policy 
```
modified : 
```
node_ajax_view.html    -->  display image view condition modified according to file mime type
node_details_base.html      
ndf_tags.py   -->   get_edit_url() defination modified ( 'file_edit' url in included for editing the document ) 
urls/file.py    
views/file.py   -->  Included file_edit() method to provide edit and save mechanism to documents
```