Logout of AdminUI

As a logged in user I want to logout of the current session so that I can login as a different user.

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Currently login is handled by BasicAuth which requires quitting the browser to invalidate the authenticated session. There are some hacky solutions with JS (eg. [1,2]) which maybe can logout from a Basic Auth session.

It would require some testing in different browser to see if it works but could potentially be quite simple addition to the Admin UI (maybe a 'logout' button/link in the ⚙️ Setting screen)

[1] https://stackoverflow.com/questions/233507/how-to-log-out-user-from-web-site-using-basic-authentication/60450491#60450491
[2] https://tuhrig.de/basic-auth-log-out-with-javascript/