Adding entity recognition and example notebook

[effyli]

Adding a named entity recognition method with huggingface. Adding an example notebook on how to use the recognizer with emails and visualize the recognized entities.

[sbenthall]

Thanks for this PR!

The failing test seems to be unrelated -- it's due to deprecation in some dependencies: https://github.com/scverse/anndata/commit/7b1077d5e1a63fef0d47d716d19ea14ad2ad10de

Once I've gotten this test fixed I'll merge this PR.

[sbenthall]

Does this code have any additional dependencies not yet included in requirements.txt?

[sbenthall]

import transformers[torch]
import contractions
import spacy

[Christovis]

As this is still in an early experimental stage, I would opt for not merging it for now and wait until this work has more matured.