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.
Does this mean that onAuth() could only be called by at most exactly one listener? It seems like, if I create an Auth service, it could be passed around to other services which might each create their own onAuth() listeners. According to this structure, offAuth would only remove the last one attached?