Add ShellDrawingArea and ShellStack

ShellDrawingArea is a size-independent wrapper for a ClutterCairoTexture.
Useful when drawing non-fixed size areas.

ShellStack is a simple container class which holds items
in a completely overlapping Z stack.  The main difference
from ClutterGroup is that items will be constrained to
(and allocated) the size of the stack, not getting their
preferred size always.

src/shell-stack.h

@@ -0,0 +1,33 @@
+#ifndef __SHELL_STACK_H__
+#define __SHELL_STACK_H__
+
+#include <clutter/clutter.h>
+#include <gtk/gtk.h>
+
+#define SHELL_TYPE_STACK                 (shell_stack_get_type ())
+#define SHELL_STACK(obj)                 (G_TYPE_CHECK_INSTANCE_CAST ((obj), SHELL_TYPE_STACK, ShellStack))
+#define SHELL_STACK_CLASS(klass)         (G_TYPE_CHECK_CLASS_CAST ((klass), SHELL_TYPE_STACK, ShellStackClass))
+#define SHELL_IS_STACK(obj)              (G_TYPE_CHECK_INSTANCE_TYPE ((obj), SHELL_TYPE_STACK))
+#define SHELL_IS_STACK_CLASS(klass)      (G_TYPE_CHECK_CLASS_TYPE ((klass), SHELL_TYPE_STACK))
+#define SHELL_STACK_GET_CLASS(obj)       (G_TYPE_INSTANCE_GET_CLASS ((obj), SHELL_TYPE_STACK, ShellStackClass))
+
+typedef struct _ShellStack        ShellStack;
+typedef struct _ShellStackClass   ShellStackClass;
+
+typedef struct _ShellStackPrivate ShellStackPrivate;
+
+struct _ShellStack
+{
+    ClutterGroup parent;
+
+    ShellStackPrivate *priv;
+};
+
+struct _ShellStackClass
+{
+    ClutterGroupClass parent_class;
+};
+
+GType shell_stack_get_type (void) G_GNUC_CONST;
+
+#endif /* __SHELL_STACK_H__ */