static: Pre-compress with zopfli, for better compression.

Zopfli[^1] performs very good, but time-intensive, zlib compression.
It is hence only suitable for pre-compressing objects, not on-the-fly
compression.

Use a webpack plugin to write pre-compressed versions of JS and CSS
assets using Zopfli, and configure nginx to serve those assets when
`Accept-Encoding: gzip` is provided.

This reduces the size of the JS and CSS assets on initial pageload
from 1422872 bytes to 1108267 bytes, or about a 22% savings.

[^1]: https://github.com/google/zopfli

package.json

@@ -8,6 +8,7 @@
     "@babel/register": "^7.6.2",
     "@fontsource-variable/open-sans": "^5.0.9",
     "@formatjs/intl": "^2.0.0",
+    "@gfx/zopfli": "^1.0.15",
     "@giphy/js-components": "^5.13.0",
     "@giphy/js-fetch-api": "^5.6.0",
     "@koa/bodyparser": "^5.0.0",
@@ -25,6 +26,7 @@
     "clean-css": "^5.1.0",
     "clipboard": "^2.0.4",
     "colord": "^2.9.3",
+    "compression-webpack-plugin": "^11.1.0",
     "core-js": "^3.37.0",
     "css-loader": "^7.1.1",
     "css-minimizer-webpack-plugin": "^7.0.0",