Add browserid auth backend
Add missing *args, **kwargs in custom save()s

It was causing errors when passing extra arguments.
Implement browserid login

Login button now defaults to using browser ID, but falls back on
django's builtin auth if javascript is disabled. Users should be able to
choose which method they want to use.
Customize login process for BrowserID

Require new users to enter a username (and optionally a first and last
name) before creating a new account.