Notebook: Wrap child properties

	* gtk/src/gtk_signals.defs: Add definitions for "tab-label",
	"menu-label", "position", "tab-expand", "tab-fill",
	"reorderable", and "detachable".
	* gtk/src/notebook.hg: Add wrappers for the aforementioned child
	properties.
demo: Update notebook's tabs style

	* demos/gtk-demo/demowindow.cc: Set "tab-expand" child property
	of "Info" and "Source" tabs, as it is currently done in
	gtk3-demo.