Add auth-later, for using auth when it is loaded

Depends on https://github.com/Livefyre/Livefyre.js/pull/6/

and 

https://github.com/Livefyre/Livefyre-scout/pull/4

DNM until testing with the above merges.
Is there a reasonable way of getting this asynchronously via Livefyre.require?

At some point I kinda would like to just remove Livefyre.auth, otherwise everyone is going to use it...