Standardize documentation sites

[jsiegle]

• Update to latest version of pydata-sphinx-theme (0.13.3)
• Standardize sidebar font colors
• Standardize fonts (h1 through h6) and link colors
• Put GitHub + Twitter + Discord links in navbar
• Standardize landing page
  • Remove large title
  • Change page title to "Home"
  • Start with large image
  • Page link cards in one row instead of 2 and remove borders
  • Remove license info
• Add LICENSE file to source code (CC-BY-SA 4.0)
• Place search bar on landing page only; otherwise it's in the navbar
• Standardize logo font and size (and add template + instructions to doc-template repo)
• Standardize HTML page names (Page Title – Project Name)
• Make sure "Edit on GitHub" and "Show Source" links are visible
• Standardize README files

Changes specific to this site

• Hide SPI commutator pages, since this device is not yet available

TODO

• Find a better image for the landing page