fix(avatars): add profile server client to proxy remote images

Fixes #1458.
Fixes #1447.
Fixes #1469. It fixes the client portion, at least. The server depends on https://github.com/mozilla/fxa-profile-server/issues/31.

Not sure if we want to merge until the server side is ready.
Ooo, good catch! Looks like that might [still be a problem](http://google-styleguide.googlecode.com/svn/trunk/javascriptguide.xml?showone=Closures#Closures).