WEB: Restructuring pages and navigation, styling and new footer
xref #28519
closes #28520

You can see the result rendered in: https://datapythonista.github.io/pandas-web/ (the new logo is not in the PR).

Been discussing with NumPy the navigation, and what is proposed here is with minimal differences agreed with them. See https://github.com/numpy/numpy.org/issues/43

I don't touch the home page here, I think we need to remove almost everything we've got so far (based on the current), and move more in the direction of Dask or Jupyter. Discussions about it better in #28168 than here.