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.
I say by default we push people to the latest library. It is backwards compatible, but I'd rather that only come up if people actually ask us about it. We need/want people to upgrade, so let's not give them any reasons to not do so.

Ultimately, when a new customer comes to AngularFire, I want them to pull down Firebase 2.0.x, not 1.1.x.