Haiku: Display: Add event listener and filter support

Code copied verbatim from the gtk implementation.
Haiku: Get basic Label support going

* HaikuWindow: Add a root view that we can control.
* Composite/HaikuView: Add some child view management.
* Add support for getting/setting the view size.
* Add basic Label support. No separators, no border, no alignment,...

This gets the HelloWorld2 example (label in shell) working, save for
the incorrect alignment.
Haiku: Label: Add support for setting the alignment