Added Gravatar support for people who supply email addresses but haven't put up an avatar. Which is no one.

...the main effect of this is that users who fail to hit anything in the gravatar DB will get a JPEG version of the default avatar instead of the fancy new PNG version, which looks white even on the dark theme. (Alas.)

In other news, you can now change the e-mail address you provided during registration, which still isn't shown publicly.

...also corrected Aino Meilani's user title.