Graph visibility, graph canvas dimensions modified and hyperlinks added ...

Changed following files : 

 - ```node_details_base.html``` - Appearance of graph wherever required and added close button to overlay.
 - ```node_graph.html``` - Changed SVG canvas dimensions. Added code to give hyperlinks to graph nodes.
 - ```ajax_views.py``` - Added ```graph_nodes()``` to make json required for graph.
 - ```ajax_urls.py``` - Added necessary url to call ```graph_nodes()```.
 - ```methods.py``` - Removed ```graph_nodes``` method.
 - ```page.py``` - Removed processing for graph in this view.