R1:60db658d52c4

Record account recovery email links in the user activity log and make the mail message reference the log

Summary:
Depends on D20672. Ref T13343. When a user requests an account access link via email:

- log it in the activity log; and
- reference the log in the mail.

This makes it easier to ban users misusing the feature, provided they're coming from a single remote address, and takes a few steps down the pathway toward a button in the mail that users can click to report the action, suspend account…