Upgrade code to support stylegan2-ada / tensorflow2

[johndpope]

This code is based on outdated 2019 code. The internals dnn folder was bumped here for 2020 https://github.com/NVlabs/stylegan2-ada

There are a bunch of fixes / support across the board. https://github.com/NVlabs/stylegan2-ada/blob/main/dnnlib/tflib/custom_ops.py

I performed a drop in / and worked on other projects because the file formats / pkl saved files are the same.

N.b. - nvidia are abandoning tensorflow and going to pytorch - I have a branch that supports tensorflow2 https://github.com/johndpope/stylegan2-ada/

more elaborate / cherry picked branch here with training support. https://github.com/johndpope/stylegan2-ada/tree/digressions