Add some research results.

wiki/src/blueprint/GNotification.mdwn

@@ -92,6 +92,6 @@
 * GNOME Shell 3.16: non-default action buttons are only displayed when
   the notification pops up initially, _not_ in the [Message
   List](https://wiki.gnome.org/Design/OS/Notifications/#Message_List).
-  - Is it the same on Jessie?
-  - Can we get away with only a default action that opens the URL we
-    want in the use cases we have in practice?
+  Jessie's GNOME Shell (3.14) hasn't this problem. We can get away
+  with only a default action that opens the URL we want, in the use
+  cases we have in practice.