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.
Use `AccountManager#getAuthToken()` instead of calling the `AuthenticatorActivity` directly. Mostly to follow convention.