* src/Makefile.am: Added glade-palette-item.[ch],
	  glade-palette-box.[ch] and glade-palette-expander.[ch]
	  to build sources.

	* src/glade.h, src/glade-builtins.[ch]: Declare an enum
	  GladeItemAppearance and define a GType for it.

	* src/glade-palette.[ch]: Entirely reworked. new API.

	* src/glade-app.c, src/glade-fixed.c,
	  src/glade-placeholder.c: Recognize new palette API.

	* src/glade-project-window.c: Added UI functionality
	  to support features in the new palette.