Replaced helmet, cors & policy w/ local implem.

The used functionality of helmet, cors & referrer-policy has been
defined in setupCors and setupHeaders.

middleware/setupCORS.js

@@ -0,0 +1,6 @@
+const openCORS = (req, res, next) => {
+  res.set("Access-Control-Allow-Origin", "*")
+  return next();
+};
+
+module.exports = openCORS;