views: correctly hide events according to the mod type

When deleting events with recurrence, we want to hide the event
widgets according to the modification type. So that selecting
e.g. subsequent in the modification type dialog hides the event,
and the subsequent ones, truly reflecting the operation that will
happen.

Currently, however, the views don't do that, and only hide the
event that was asked to be deleted.

Fix that by passing the object modification type, and adapting the
views to take that into account.

src/gcal-utils.h

@@ -157,4 +157,8 @@ gboolean        ask_recurrence_modification_type                (GtkWidget
 
 gboolean        is_workday                                      (guint	                day);
 
+GList*          filter_event_list_by_uid_and_modtype            (GList                 *widgets,
+                                                                 GcalRecurrenceModType  mod,
+                                                                 const gchar           *uid);
+
 #endif // __GCAL_UTILS_H__