Splash screen's behavior in HomeAutomation is not ideal with 2.0

Running the HomeAutomation demo shows that the splash screen now disappears almost instantly, while we still see an empty screen for some time, defying its purpose.

We should check if the presentationReady is really emitted at the ideal time. (Qt3D's asynchronous nature makes things very different from 1.x in this respect) One idea is that we could probably get much better looking results if it would be tied to the first QFrameAction invocation.