More updates to Node.js example code

[keerlu]

Some more updates to the example code that could do with another quick sanity check (sorry, should have waited until I finished the tutorial draft):

• remove body-parser (deprecated) and use built-in Express parser
• include welcomeMessage in user data
• make IDs strings
• remove async defer from script import (seems a bit weird)

[csmeyns]

Yes, helpful changes, these indeed make it yet clearer and cleaner 🙂 (just for completeness: I didn't test it out from scratch this time but have read through the changes)