Serving mode UI

@MariusVolkhart The basic UI for serving mode is in there along with some of the client-side login stuff. Right now there is no communication with our API, but it does login through Twitter/Facebook and store credentials with the account manager. 

If you want to just go over this and keep the branch open to continue using it for the network stuff, that's cool. Otherwise we could just make a new branch for that, either way is fine with me.
I would rather you not modify this class. If in the future the maintainer changes the official implementation to use fragments we can't easy go and swap out. Also, it makes it more difficult to track changes that we make vs the upstream. It's also more difficult to pull this project into it's own repo b/c it relies on the BuildConfig parameters which is not a good practice for libraries since they can change across dev machines.

That being said, I am a fan of the methods you added. Perhaps extend the `SocialNetworkManager` class instead?