Add gitignore and use pip-style requirements

[2trvl]

Use pip-style requirements, because it's common

Now users can run DIS with standard python tools:

python -m venv venv
venv\Scripts\activate
pip install -r IS-Net\requirements.txt
python IS-Net\Inference.py
deactivate

Also to use different python version:

pip install virtualenv
python -m virtualenv -p "C:\Program Files\Python38\python.exe" venv