feat: pick username

* put new registered social login user to session data
* ask to choose username
* simplify checkUsername functions

server/src/middleware/authRequired.js

@@ -1,5 +1,5 @@
 export default function authRequired(req, res, next) {
-  if (req.isAuthenticated()) {
+  if (req.isAuthenticated() && !req.session.newUser) {
     next()
     return
   }