unlockDialog, loginDialog: Add a 'wake-up-screen' signal

The signal is currently present in the notifications box, but next
commits will move the notifications box to the unlock dialog.

Add a 'wake-up-screen' signal to the dialogs.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/872

js/ui/unlockDialog.js

@@ -53,7 +53,10 @@ class UnlockDialogClock extends St.BoxLayout {
 });
 
 var UnlockDialog = GObject.registerClass({
-    Signals: { 'failed': {} },
+    Signals: {
+        'failed': {},
+        'wake-up-screen': {},
+    },
 }, class UnlockDialog extends St.Widget {
     _init(parentActor) {
         super._init({