view: add :will_add_event vfunc and stub methods

Note: this commit probably won't build, but this is the right order of
keeping history.

src/gcal-week-view.c

@@ -156,6 +156,9 @@ static gboolean       gcal_week_view_draw_event            (GcalView       *view
 static GtkWidget*     gcal_week_view_get_by_uuid           (GcalView       *view,
                                                             const gchar    *uuid);
 
+static gboolean       gcal_week_view_will_add_event        (GcalView        *view,
+                                                            GcalEventWidget *event);
+
 G_DEFINE_TYPE_WITH_CODE (GcalWeekView,
                          gcal_week_view,
                          GTK_TYPE_CONTAINER,
@@ -234,6 +237,8 @@ gcal_view_interface_init (GcalViewIface *iface)
   iface->draw_event = gcal_week_view_draw_event;
   iface->get_by_uuid = gcal_week_view_get_by_uuid;
   /* iface->clear = gcal_week_view_clear; */
+
+  iface->will_add_event = gcal_week_view_will_add_event;
 }
 
 static void
@@ -1410,6 +1415,13 @@ gcal_week_view_get_by_uuid (GcalView    *view,
   return NULL;
 }
 
+static gboolean
+gcal_week_view_will_add_event (GcalView        *view,
+                               GcalEventWidget *event)
+{
+  ;
+}
+
 /* Public API */
 /**
  * gcal_week_view_new: