Grpah feature: Shift+click to fix the node position in the graph

In the node_graph.html.

1) var flag;
    - This variable is used for the node fix position by default it's false.

2) function dblclick
    - This function will reset the node position.

3) function ondrag
    - This fuction will check flag if flag is true it will be fix the position of node other wise it will not fix the position.