R1:deb80b7652f7

Provide an activity log for login and administrative actions

Summary: This isn't complete, but I figured I'd ship it for review while it's still smallish.

Provide an activity log for high-level system actions (logins, admin actions). This basically allows two things to happen:

- The log itself is useful if there are shenanigans.
- Password login can check it and start CAPTCHA'ing users after a few failed attempts.

I'm going to change how the admin stuff works a little bit too, since right now you…