Refactor module (loader) rules

- Removed unnecessary url-loader targeting .woff files
- Replaced file-loader with url-loader (file is fallback for url)
- PostCSS plugins are all loaded manually vs postcss.config.js

resources/assets/build/postcss.config.js

@@ -0,0 +1,15 @@
+/* eslint-disable */
+
+const cssnanoConfig = {
+  preset: ['default', { discardComments: { removeAll: true } }]
+};
+
+module.exports = ({ file, options }) => {
+  return {
+    parser: options.enabled.optimize ? 'postcss-safe-parser' : undefined,
+    plugins: {
+      cssnano: options.enabled.optimize ? cssnanoConfig : false,
+      autoprefixer: true,
+    },
+  };
+};