tweak quick-help

- increase maximum height of dialogs
- toggle display of the help dialog, only create it once.

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

@@ -66,4 +66,8 b' span#login_widget {'
 
 #header > span {
   margin-top: 10px;
-}
  No newline at end of file
+}
+
+.modal-body {
+  max-height: 500px;
+}

IPython/frontend/html/notebook/static/notebook/js/quickhelp.js

@@ -19,8 +19,7 b' var IPython = (function (IPython) {'
         var that = this;
         if ( this.shortcut_dialog ){
             // if dialog is already shown, close it
-            this.shortcut_dialog.find("button").first().click();
-            this.shortcut_dialog = null;
+            $(this.shortcut_dialog).modal("toggle");
             return;
         }
         var body = $('<div/>');
@@ -60,6 +59,7 b' var IPython = (function (IPython) {'
         this.shortcut_dialog = IPython.dialog.modal({
             title : "Keyboard shortcuts",
             body : body,
+            destroy : false,
             buttons : {
                 Close : {}
             }

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

@@ -1057,6 +1057,7 b' span#login_widget{float:right;}'
 .nav-header{text-transform:none;}
 .navbar-nobg{background-color:transparent;background-image:none;}
 #header>span{margin-top:10px;}
+.modal-body{max-height:500px;}
 @font-face{font-family:'FontAwesome';src:url('../components/font-awesome/build/assets/font-awesome/font/fontawesome-webfont.eot?v=3.1.0');src:url('../components/font-awesome/build/assets/font-awesome/font/fontawesome-webfont.eot?#iefix&v=3.1.0') format('embedded-opentype'),url('../components/font-awesome/build/assets/font-awesome/font/fontawesome-webfont.woff?v=3.1.0') format('woff'),url('../components/font-awesome/build/assets/font-awesome/font/fontawesome-webfont.ttf?v=3.1.0') format('truetype'),url('../components/font-awesome/build/assets/font-awesome/font/fontawesome-webfont.svg#fontawesomeregular?v=3.1.0') format('svg');font-weight:normal;font-style:normal;}[class^="icon-"],[class*=" icon-"]{font-family:FontAwesome;font-weight:normal;font-style:normal;text-decoration:inherit;-webkit-font-smoothing:antialiased;*margin-right:.3em;}
 [class^="icon-"]:before,[class*=" icon-"]:before{text-decoration:inherit;display:inline-block;speak:none;}
 .icon-large:before{vertical-align:-10%;font-size:1.3333333333333333em;}