This widget is far from finished, but it's off to a good start.
Also added a GResizeEvent and GWidget::resize_event() so that widgets
can react to being resized.
To start painting, call:
gui$get_window_backing_store()
Then finish up with:
gui$release_window_backing_store()
Process will retain the underlying GraphicsBitmap behind the scenes.
This fixes racing between the WindowServer and GUI clients.
This patch also adds a WSWindowLocker that is exactly what it sounds like.
