R1:30f6405a8654

Add an explicit temporary token management page to Settings

Summary:
Ref T5506. This makes it easier to understand and manage temporary tokens.

Eventually this could be more user-friendly, since it's relatively difficult to understand what this screen means. My short-term goal is just to make the next change easier to implement and test.

The next diff will close a small security weakness: if you change your email address, password reset links which were sent to the old address are still valid. Although…