tensorflow 2.x and python 3.9 compatiblities

[wooyeonkwon]

codes and their related modules have edited for tensorflow 2.x

keras module has combined with tensorflow 2.x

So, we should use keras module in the tensorflow.

And, In python 3.9 we should allow pickle option when we load *.npy.

However it can read all files including '.gitignore' file.

So, I made some filter for loaders.py module

env.yaml has updated for new HYU server environment (py39-cuda12.8).

[wooyeonkwon]

update README. Prerequisite and conda env name have been changed.
We can also use common env with "export CONDA_ENVS_PATH=/opt/anaconda3/envs/:$CONDA_ENVS_PATH"
py39-cuda12.8 environment supports all modules we need.

[wooyeonkwon]

CONDA_ENVS_PATH has been set as global environment. Need not to execute export ...
update README and clear ipynb.