subscriber: added protected internal structure

The idea here is to make GcalSubscriber handle the container
responsibilities of the view, and the view will handle only the drawing
an allocating, this would allow us to remove GcalView interface and
merge its methods in GcalSubscriber.

src/gcal-subscriber.h

@@ -21,6 +21,7 @@
 #define __GCAL_SUBSCRIBER_H__
 
 #include "gcal-manager.h"
+#include "gcal-event-widget.h"
 
 #include <gtk/gtk.h>
 
@@ -35,15 +36,22 @@ G_BEGIN_DECLS
 
 typedef struct _GcalSubscriber                       GcalSubscriber;
 typedef struct _GcalSubscriberClass                  GcalSubscriberClass;
+typedef struct _GcalSubscriberPrivate                GcalSubscriberPrivate;
 
 struct _GcalSubscriber
 {
   GtkContainer parent;
+
+  GcalSubscriberPrivate *priv;
 };
 
 struct _GcalSubscriberClass
 {
   GtkContainerClass parent_class;
+
+  /*< public >*/
+  gboolean  (*is_child_multicell) (GcalSubscriber *subscriber, GcalEventWidget *child);
+  guint     (*get_child_cell)     (GcalSubscriber *subscriber, GcalEventWidget *child);
 };
 
 GType          gcal_subscriber_get_type         (void);