hide header-bar when header is hidden

also reduce the amount of CSS used to accomplish the 1px line (no negative margins)

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

@@ -33,9 +33,8 b' div#header {'
 
     .header-bar {
         width: 100%;
-        height: 0px;
-        border-bottom: 1px solid @navbar-default-border;
-        margin-bottom: -1px;
+        height: 1px;
+        background: @navbar-default-border;
     }
 
     @media print {

IPython/html/static/notebook/js/menubar.js

@@ -207,7 +207,8 b' define(['
         
         // View
         this.element.find('#toggle_header').click(function () {
-            $('div#header-container').toggle();
+            $('#header-container').toggle();
+            $('.header-bar').toggle();
             that._size_header();
         });
         this.element.find('#toggle_toolbar').click(function () {

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

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

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

@@ -8283,9 +8283,8 b' div#header #header-container {'
 }
 div#header .header-bar {
   width: 100%;
-  height: 0px;
-  border-bottom: 1px solid #e7e7e7;
-  margin-bottom: -1px;
+  height: 1px;
+  background: #e7e7e7;
 }
 @media print {
   div#header {
@@ -10267,7 +10266,6 b' select[multiple].celltoolbar select {'
   box-sizing: border-box;
   -moz-box-sizing: border-box;
   -webkit-box-sizing: border-box;
-  margin-top: 1px;
 }
 #menubar .navbar {
   border-top: 1px;