Switch from Webpacker to cssbundling-rails, upgrade Tailwind

tailwind.config.js

@@ -0,0 +1,17 @@
+module.exports = {
+  content: [
+    './app/views/**/*.html.erb',
+    './app/helpers/**/*.rb',
+    './app/javascript/**/*.js'
+  ],
+  theme: {
+    extend: {
+      fontFamily: {
+        sans: ['Open Sans', 'sans-serif']
+      }
+    },
+  },
+  plugins: [
+    require('@tailwindcss/forms')
+  ],
+}