Backport PR #8174: add 4px between notification areas

![screen shot 2015-03-27 at 15 25 37](https://cloud.githubusercontent.com/assets/151929/6878113/aeb2ddfc-d495-11e4-94c9-9059723033a7.PNG)

closes  #7790

cc: @ellisonbg

IPython/html/static/notebook/less/notificationwidget.less

@@ -2,6 +2,7 b''
     color: @navbar-default-link-color;
     z-index: 10;
     background: @notification_widget_bg;
+    margin-right: 4px;
     .btn-default();
 }
 

IPython/html/static/style/style.min.css

@@ -10882,6 +10882,7 b' ul#help_menu li a i {'
   color: #777777;
   z-index: 10;
   background: rgba(240, 240, 240, 0.5);
+  margin-right: 4px;
   color: #333333;
   background-color: #ffffff;
   border-color: #cccccc;