This patch adds two new API's:
- WidgetType& GUI::Window::set_main_widget<WidgetType>();
This creates a new main widget for a window, assigns it, and returns
it to you as a WidgetType&.
- LayoutType& GUI::Widget::set_layout<LayoutType>();
Same basic idea, creates a new layout, assigns it, and returns it to
you as a LayoutType&.
Previously it was only possible to change these window attributes when
creating a new window. This patch adds an IPC message that allows you
to change them at runtime.
We were not repainting windows that were occluded at the time of the
theme changing. This patch adds a way to bypass occlusion testing when
invalidating window rects.
Fixes#1249.
