manager: set client upon loading event

Add EClient support while loading an event.
This EClient then helps us check its
capability in window.

https://bugzilla.gnome.org/show_bug.cgi?id=782755

src/gcal-manager.c

@@ -380,6 +380,8 @@ on_client_connected (GObject      *source_object,
       return;
     }
 
+  g_object_set_data (G_OBJECT (source), "client", client);
+
   unit = g_new0 (GcalManagerUnit, 1);
   unit->connected = TRUE;
   unit->client = g_object_ref (client);