Wait at least 2 seconds before leaving Splash Screen

Use jDeferred for promises, in order to wait until *both* the AJAX request
has finished *and* 2 seconds have elapsed

Fixes #94
Since the deferred is resolved with the response from ``autoLogin(cb)`` I think ``autoLoginDeferred`` is a reasonable, meaningful name.

We may want to rename ``promise`` to ``autoLogin`` so that this line is maximally expressive:

```java
autoLogin.done(new DoneCallback<Bundle>() { ... });