Add Desired-edge-length Guided (DELG) Layout option

[bherr2]

Add the DELG layout algorithm as an option/alternative to the BatchTree Algorithm.

Notes from the DELG author ( @abureyanahmed ):

To run the code of our desired edge length guided algorithm go to:
https://github.com/abureyanahmed/multi_level_tree

The code of the algorithm is in the "desirable_length_guided" folder. To run the algorithm you need to create some javascript files. Take a file from the "dataset/" folder. Then run it with the "print_javascript_data_topics.py" file which will print the necessary js objects, store them into a js file. Then import it in the "avoiding_crossing_by_initialization.html" file using a script tag. Open the html file in a browser and you will be able to run the algorithm and download the output.

Please let me know if you have any questions.

Thanks,
Reyan

[bherr2]

Example code to convert .dot to it's input and output to .dot is provided at https://colab.research.google.com/drive/1iJDwpxmYhlugCCj3iK4TpjVNyv1wi72Q?usp=sharing

[bherr2]

Updated code to work with Node.js is here: https://github.com/abureyanahmed/DELG