Move to server-based dev environment

[rdmurphy]

The "render everything in dev" approach is outdated and has become untenable in major projects such as the coronavirus tracker and elections. There are a lot of little details that'd go into getting this right, but it's time to get serious about having pages and assets build/render on the fly based on the page that's currently being viewed.

New features like the {% asset %} tag are already a move more toward doing work as needed instead of ahead of time. CSS/SCSS processing and JS processing will also have to be reworked to be more compatible with this, but overall this is the direction we should go anyway for UX reasons.

The biggest question IMO is whether this attempts to land independent of the major changes happening in the next branch or not.