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.
This could throw a number of errors. Maybe should catch them and at least log/rethrow to help devs. Maybe just catch...

At the very least if auth[methodCall] is not a function that is worth complaining about.