Switchable views

Add a trivial controller that switches between two views now defined in the application.

This should be almost enough structure for arbitrary paths through the views of the final app. One area where it may still fall short is that it implies only a single exit from each view when in reality several views probably have several exits. I think the step from here to there is smaller than the step from current main to this branch though (it's basically just more complex logic for handling values in the Events here, not structurally different).