Upgrade gulp and webpack

[sondr3]

• Look to Googles Web Starter Kit and other for how things look today
• Upgrade straight away to Webpack 4
• Figure out where to use what and when

Food for thought

We could probably get away with just using Webpack for bundling CSS, images and JS etc and then having a few NPM scripts that run that'll keep everything synced up nicely. For example:

"scripts": {
    "predev": "jekyll build --watch --incremental",
    "dev": "webpack --watch --i-dont-know-webpack"
}

Would first start Jekyll, and have it watch the src/ directory in the background and then start up Webpack with it's dev server and such. Similarly, we'd have a command for when you want to optimize everything, probably called prod or something like that. We'll have to look into it.