Update the code to Python 3

[HumamAlwassel]

DETAD code is in Python 2 and might not be compatible in a straightforward way with Python 3.

Action items:

• update the conda environment packages, such as Python, numpy, and matplotlib
• remove legacy syntax specific to only Python 2
• verify that results on the example files are not changed

[HumamAlwassel]

The code is upgraded to Python 3 as of commit def334f6cd385aff860adfb7bbe9db8d3b2c3ec2