Remove dependency on pytorch / tensorflow for default install of DIANNA

[stefsmeets]

The default dianna install is quite large because of dependencies on tensorflow and pytorch. These dependencies are not necessary to run dianna. But it makes it very slow to install and the virtualenvironment is very large (6-7 GB).

It will improve the user experience if the default install of dianna is quite lean.

We could separate the dependencies where necessary in subpackages:

pip install dianna
pip install dianna[dashboard]
pip install dianna[tutorials]
...

[stefsmeets]

I removed torch / tensorflow from the default install. It makes it really clear what the difference in install size is.

My venv before installing torchtext:

(.venv) stef@debian:~/python/dianna $ du -hd0 .venv
779M	.venv

My venv after installing torchtext:

(.venv) stef@debian:~/python/dianna $ du -hd0 .venv
5.0G	.venv

[stefsmeets]

onnx_tf requires tensorflow and tensorflow_probabilities, but it does not declare them as dependencies.