Panoptes.js Experimental Auth: add signOut()

[shaunanoordin]

PR Overview

Package: Package: lib-panoptes-js
Part of: replacing PJC with Panoptes JS
Follows and requires: #6552

This PR continues the experiment to remove PJC from FEM. We now have the ability to Sign Out from the Zooniverse!

• Experimental Auth: added signOut()
  • signOut() will sign the user out of the Panoptes server, and reset the data store. Returns true on success.
  • ⚠️ Note one difference in the behaviour of the new signOut() vs old PJC signOut.
    • New: if a user isn't signed in, signOut() exits with return false.
    • Old: if a user isn't signed in, signOut() throws an error.
    • I personally don't think attempting to sign out while not signed in is bad enough to throw an error, but I'm happy to discuss this. I may be missing actual use cases where thrown errors would be appropriate.
• Dev server: new "sign out" button added, to manually trigger the action.

Status

Ready for internal team review.

Again, please note that the code is verbose on purpose.

For an overall overview of the auth, please see "Understanding Auth with Panoptes.js & PJC": https://docs.google.com/presentation/d/1KwqAjUcFa7QENV2N-qpDs7deILp_nIHl_K-ZBx8G9K4/edit (Zooniverse team only)