Make headerbar -1 margin global

IPython/html/static/base/less/page.less

@@ -35,6 +35,7 b' div#header {'
         width: 100%;
         height: 0px;
         border-bottom: 1px solid @navbar-default-border;
+        margin-bottom: -1px;
     }
 
     @media print {

IPython/html/static/notebook/less/menubar.less

@@ -1,5 +1,6 b''
 #menubar {
   .border-box-sizing();
+  margin-top: 1px;
 
   .navbar {
     border-top: 1px;

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

@@ -76,13 +76,6 b' p {'
     height: 200px;
 }
 
-.lower-header-bar {
-    width: 100%;
-    height: 0px;
-    border-bottom: 1px solid @navbar-default-border;
-    margin-bottom: -1px;
-}
-
 .notebook_app #header {
     .box-shadow(@global-shadow);
 }

IPython/html/static/terminal/less/terminal.less

@@ -4,10 +4,6 b''
   #header {
     background: @body-bg;
     .box-shadow(@global-shadow);
-
-    .header-bar {
-      margin-bottom: -1px;
-    }
   }
 
   .terminal {