Add nodemon config

This makes the "npm start" and "npm run dev" commands work again and
restart the dev environment when the Webpack configuration changes.
Copied from the current repository

nodemon.json

@@ -0,0 +1,8 @@
+{
+   "watch": [
+	   "webpack.config.js",
+	   "webpack.production.js",
+	   "campaign_info.toml"
+   ],
+   "exec": "webpack serve --host 0.0.0.0"
+}