Create a production build of Tailwind at release time (#292)

* Add support for purging tailwind styles. For #224

* Build prod version of tailwind in build script

build/javascript/postcss.config.js

@@ -0,0 +1,7 @@
+module.exports = {
+  plugins: [
+    require('cssnano')({
+      preset: 'default',
+    }),
+  ],
+};