display: Export the timestamp of the event as well

When passing on keybindings, make sure to pass the timestamp
of the event as well as the deviceid and the action.

https://bugzilla.gnome.org/show_bug.cgi?id=704858

src/core/display-private.h

@@ -460,7 +460,8 @@ void meta_display_remove_autoraise_callback (MetaDisplay *display);
 void meta_display_overlay_key_activate (MetaDisplay *display);
 void meta_display_accelerator_activate (MetaDisplay *display,
                                         guint        action,
-                                        guint        deviceid);
+                                        guint        deviceid,
+                                        guint        timestamp);
 gboolean meta_display_modifiers_accelerator_activate (MetaDisplay *display);
 
 /* In above-tab-keycode.c */