Migrating to the PyData theme for the online docs

[maximelucas]

This switches the theme of the onlines docs to the PyData theme.

Some reorganization is needed to fit with the theme.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.13%. Comparing base (7335eca) to head (5f56d6c).
Report is 54 commits behind head on main.

Additional details and impacted files

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  Coverage   93.13%   93.13%           
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  Files          60       60           
  Lines        4503     4503           
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  Hits         4194     4194           
  Misses        309      309           

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[nwlandry]

I won't have the chance to do a thorough review by the time you need it, but overall looks great! Thanks for making this happen!

Quick things I noticed:

• where is the using XGI page?
• XGI-DATA table looks funky in dark mode
• "Copyright Copyright" in the footer
• In the side bar under API, "Linear Algebra" instead of "Linalg" and might want to revisit other names as well for maximum explainability?
• In the API sidebar, do we really need the full path of all modules? It's pretty verbose.

I really like what you did with the installation guide and the tutorials!

[maximelucas]

Thanks for the quick initial review Nich!

• "projects using XGI" page is linked to in text of the home page.
• good catch, I disabled the mode switch for now
• about the paths, I managed to shorted them for the functions, but not the module paths in the toc (it was like that in our current online docs already). I suggest we can try again in another PR

[maximelucas]

Summary of what I did for the record:

• New 1-level structure is now: Homepage, Installing, User Guides, API Reference, XGI-DATA, Gallery, and Development
• Homepage: is now more concise (I moved some sections in other places and linked them)
• Installing: concise but links to a "more options" page
• User Guides: new page, presenting the categories of tutorials
• API Ref: added a small description of the API at the top
• XGI-Data: added link to documentation (fix cannot easily find the functions for loading the datasets in the docs? #548)
• Development: now combines "Contribute" and "Contributors"

I have ideas of options of things to add in the future, maybe a page for Releases, a better Gallery, etc.

[nwlandry]

Can you restore using-xgi in the sidebar?