screenShield: Add some padding between the clock and notifications box

https://bugzilla.gnome.org/show_bug.cgi?id=685919

data/theme/gnome-shell.css

@@ -2234,6 +2234,10 @@ StScrollBar StButton#vhandle:active {
     -arrow-shadow: 0 1px 1px rgba(0,0,0,0.4);
 }
 
+.screen-shield-contents-box {
+    spacing: 48px;
+}
+
 .screen-shield-clock {
     color: white;
     text-shadow: 0px 1px 2px rgba(0,0,0,0.6);

js/ui/screenShield.js

@@ -726,7 +726,8 @@ const ScreenShield = new Lang.Class({
                                                          y_align: Clutter.ActorAlign.CENTER,
                                                          x_expand: true,
                                                          y_expand: true,
-                                                         vertical: true });
+                                                         vertical: true,
+                                                         style_class: 'screen-shield-contents-box' });
         this._clock = new Clock();
         this._lockScreenContentsBox.add(this._clock.actor, { x_fill: true,
                                                              y_fill: true });