Dependency Maintenance

* Start using the [pnpm](https://pnpm.io/) package manager rather than npm.
* Replace `node-sass` with `sass`.
* Update versions of many dependencies
* Didn't yet update webpack to v5, since that'll be a mess.
* Clean some old build scripts out of package.json

.eslintrc.js

@@ -13,7 +13,7 @@ module.exports = {
 		'react'
 	],
 	'parserOptions': {
-		'parser': 'babel-eslint',
+		'parser': '@babel/eslint-parser',
 		'ecmaVersion': 8,
 		'sourceType': 'module',
 		'ecmaFeatures': {