Add snazzy splash page

[peytondmurray]

This PR adds a snazzy landing page with some nice buttons to the major areas of the site. Additionally,

• As I was adding this I disabled the secondary sidebar for the index (probably don't want it).
• :point_up: This broke the JS that handles the modal that we use for displaying git history, so I fixed that
• I added a function in conf.py that allows us to include static assets on a per-page basis, and to render specific pages with certain templates. I used this to render the index with the snazzy buttons

[peytondmurray]

Had some feedback on the discord server, so I'm considering this approved. Merging.