Make repeated notifications less intrusive

[pyBlob]

• I keep getting this popup, even though the last update on github happened more than an hour ago:
  "A new version of Source Academy is available. Please refresh the browser."
• I opened the network tab, to see whether it performs a request that checks for an update. Though, that does not seem to be the case. It just opens the popup.
• Loading the page with "Disable cache" fetches all new pages, but the popup still keeps showing up.

This is annoying while reading the book, and the popup may even stack multiple times.

I would suggest to get rid of this popup entirely, and just force a reload when the user clicks on a link to navigate to the next chapter?

Edit: After having to reload the browser, because the goto definition on the huge pretty-printed main.js locked up everything ... The popup is gone? 🤔

[RichDom2185]

It seems like the main issue is not with the popup appearing, but instead, our handling/stacking of multiple notifications (e.g. "A new version", 401/403 errors), that can be intrusive to the user experience.