widen modal dialogs on wide displays

needed for quick help layout with multiple meta keys

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

@@ -81,3 +81,10 b' span#login_widget {'
 .modal-body {
   max-height: 500px;
 }
+
+@media (min-width: 768px) {
+  .modal {
+      width: 700px;
+      margin-left: -350px;
+  }
+}

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

@@ -1303,7 +1303,7 b' span#login_widget{float:right}'
 .navbar-nobg{background-color:transparent;background-image:none}
 #header>span{margin-top:10px}
 .modal-body{max-height:500px}
-.center-nav{display:inline-block;margin-bottom:-4px}
+@media (min-width:768px){.modal{width:700px;margin-left:-350px}}.center-nav{display:inline-block;margin-bottom:-4px}
 .alternate_upload{background-color:none;display:inline}
 .alternate_upload.form{padding:0;margin:0}
 .alternate_upload input.fileinput{background-color:#f00;position:relative;opacity:0;z-index:2;width:295px;margin-left:163px;cursor:pointer;height:26px}