Add Compactness Guided (CG) Layout option

[bherr2]

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

Code is at https://github.com/tiga1231/zmlt/ and maintained by @tiga1231

[bherr2]

Update: the refactored code that can work on command line is at https://github.com/abureyanahmed/CG

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