Make package ready and upload on PyPI

This could be complicated by the fact that the installation of PyTorch-Geometric is not as trivial as `pip install torch-geometric`.

This is particularly true for the `torch-scatter`, `torch-sparse`, ... dependencies of `torch-geometric`. For these packages, [it seems like](https://pytorch-geometric.readthedocs.io/en/latest/notes/installation.html#installation-via-pip-wheels) wheels are not on PyPI but must be found instead on `https://data.pyg.org/whl/torch-${TORCH}+${CUDA}.html`.

Notice that we do need such dependencies for our project:
https://github.com/BlueBrain/morphoclass/blob/72f59fad5dca9eb08a5752a21de7577c47f1011b/install.sh#L54-L57