Visualize the graph from files in pgm formats

[gargshashank5]

1. User uploads a file from browser. Check it for [https://github.com/Implementing reading from and writing to various file formats pgmpy#65
   ](file type)
2. Parse the file using the existing reader classes for various file formats.
3. Populate a json object in the defined https://github.com/pgmpy/pgmpy_viz/wiki/Detailed-Description#214-posting-the-model with the parsed data.
4. Send the json to browser.
5. Interpret the json and show the graph.