Implemented graph with nroer graph script

Replaced previous graph structure with nroer graph script with following changes :

 - Added new method in methods.py
```
   -  For generating json file, required for graph.
   -  Some change of code in page.py file
```

- Added template and js file required for node_graph.html
```
   - Included js script from nroer - display.html file with required changes.
   - Included underscore.js file required for graph
```