Display user avatars using their actual email adress

[abompard]

In the Badges system, everybody's "email" address is [email protected], because users are keyed on email addresses and not nicknames. But FAS has the actual email address that a user may have set their libravatar on. Tahrir should ask FASJSON what the user's actual email address is to build the libravatar URL. This request should be cached for a reasonable amount of time (or, to be fancier, invalidated by fedbadges when a FAS message comes in about a user changing their email address).