migrate date and datetime widgets

packages/netlify-cms-widget-date/webpack.config.js

@@ -0,0 +1,17 @@
+const { getConfig } = require('../../scripts/webpack.js');
+
+const baseWebpackConfig = getConfig();
+
+module.exports = {
+  ...baseWebpackConfig,
+  module: {
+    rules: [
+      ...baseWebpackConfig.module.rules,
+      {
+        test: /\.css$/,
+        include: [/react-datetime/],
+        use: ['to-string-loader', 'css-loader'],
+      },
+    ],
+  },
+};