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 was playing with views the other day and learned something here. Activities have a default root view w/ the id `android.R.id.content`. It's a `FrameLayout` into which everything else gets placed. So what I'm doing here is actually redundant, b/c the `activity_authenticator` layout has a `FrameLayout` at it's root. The better approach is to either use a `<merge>` tag in the XML or to not use `setContentView()` and to instead programmatically add the fragment: `getFragmentManager().beginTransaction().add(android.R.id.content, new LoginFragment()).commit();`.

Here you can see what the view tree looks like when inflating the current XML:
![screen shot 2014-10-08 at 10 43 41 pm](https://cloud.githubusercontent.com/assets/1709517/4570894/dc8f1f50-4f67-11e4-8f7f-dc5c4a4c3d0c.png)

And here it is when adding the fragment programmatically:
![screen shot 2014-10-08 at 10 46 17 pm](https://cloud.githubusercontent.com/assets/1709517/4570901/fcef428e-4f67-11e4-83cf-152c602a9235.png)

The top main branch has 1 less view the second time around.