Revert "Modern marimo and a fancy webpage"

[mscolnick]

Reverts #8

Sorry @tschm - im reverting this change.

1. the new UI is a bit distracting - i want it simple so someone can fork and adjust (they don't need the footer and links to marimo itself)
2. i don't like make its another tool that now people need to use and i don't want to subscribe them to new tools
3. the homepage is no longer dynamic. ideally a user can just drop in their notebooks and they get a free UI

im open to the other changes like removing requirements.txt and modernizing marimo, but in another PR

[tschm]

sorry, I didn't realize my template for the index has the subpages hardcoded. That's indeed a bummer