New theme, PyData

[bruAristimunha]

Related with #352.

I still need to improve another part of doc. Improve user journey, color system, add text on new modules (braindecode, tensorflow, codecarbon).

Maybe better organize the flow and differentiate between gallery and tutorial.

Refactoring the readme

[bruAristimunha]

The new documentation is alive! Please review. I wrote a looot of new things... so we need to validate the small steps.

Since this PR focuses on documentation migration, I wish we didn't focus so much on designing things that can be improved later to speed up the release.

In summary, I reorganized the readme, installed several new dependencies for documentation, and completely refactored the config.py that generates the documentation.

I made some space adjustments, created some pictures for moabb, re-made the logo with a vectorized option, turned the tables into something dynamic, created a new section for installation, and wrote the installation tutorials and an overview section.

Much of the text is based on braindecode, mne, pandas and monai.

[sylvchev]

Brilliant! The new doc is so nice, really much more clear and organized.

[bruAristimunha]

I updated the doc, it's done, for me, it's fine for the merge

[sylvchev]

Eternal thanks @bruAristimunha 🔥