Improvement/update to 2022

[Sid1057]

Minor fixes for comfortable usage

• updated for use in TF >= 2.0 with tf2 tf_upgrade_v2
• added 'src' argument to try network for video
• added aspect ratio saving to reach best quality
• renamed webcam.py to demo.py
• fixed too small imshow window
• fixed pep8 styleguide errors
• updated readme

[Aatmaj-Zephyr]

@mattpoggi Can you please look at the request? Upgrading to Tenserflow 2 will be very useful.