Haiku: Add layout support

* Prefix callback methods with "haiku".
* Move callback methods for frame moved/resized events down to Widget.
  Also pass the new values as arguments.
* Only emit SWT.Move/SWT.Resize events in the callbacks for Shell. Only
  those can (currently) be moved/resized by the user. For programmatic
  changes we'll go through setBounds() which already emits the events
  synchronously.
* Add layout support. Mostly copied verbatim from the gtk code.

Gets the HelloWorld4 example working.