Development: tune development process

[agjohnson]

Currently, there is a singular development process for CSS, JS, and authoring site content, using Webpack. This works great if you are set up to work on everything already. If you only care about authoring content, and don't need to touch CSS or JS, or don't have the proper Node base environment, then there could potentially be some conflict here.

For now, I'd much prefer to have a singular method of contributing here. Webpack will always be used for doing development on CSS + JS, and so I prefer to also use it to build and serve Pelican content.

There are a few options here, but I'd rather not explore them yet. Just noting this for now and we can continue to tweak the process if necessary.

Raised in #132