Updated authentication methods to login v2

@katowulf - Please review but **do not merge**. I want to get your thoughts on everything up to this point. There is still more work to be done here: testing (I am going to need to updated `mockfirebase` first...), removing Simple Login code, taking authentication out of this user management file, etc. Please provide any feedback on how things are structured though.
@jwngr @katowulf 
Pretty sure this is not going to deregister the callback.
[Bound functions are not equal to their ubound counterparts](http://plnkr.co/edit/MHVgRhdjUqqFmKftcbRE?p=preview).