DOC: switch theme to new PySAL standard

[martinfleis]

Switching the theme and the structure. momepy docs still live on ReadTheDocs and a custom domain, so I'll need to figure out a best way of moving that to GitHub Pages to get a full control of what is happennign and make the version switcher working.

It is also a question how long does the execution take, it will likely take a while.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.2%. Comparing base (4037c70) to head (f7d0fa4).
⚠️ Report is 144 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #745     +/-   ##
=======================================
+ Coverage   97.4%   98.2%   +0.9%     
=======================================
  Files         26      28      +2     
  Lines       4328    4333      +5     
=======================================
+ Hits        4214    4257     +43     
+ Misses       114      76     -38     

Files with missing lines	Coverage Δ
momepy/streetscape.py	97.6% <ø> (ø)

... and 19 files with indirect coverage changes

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[martinfleis]

gh-pages in ready here - https://pysal.org/momepy. I'll just need to figure out the domain but that can wait a bit. Gonna fix the linting and it is probably ready to go.

[martinfleis]

Ignore failing RTD, that is going away.

[martinfleis]

All above should be fixed now. I have dropped existing contributing guide and used the one from gwlearn as it is simpler.

On the data frame output width, I fixed CSS so it is horizontally scrollable like in the old docs.

Again, some of the changes will need to propagate across the federation but I'd wait until it is all ironed out.