schedule/events: keep table header always visible

FixedHeader extension makes table header always visible - it stays on
top of page while user scrolls page.

Author: hrw

layouts/main.html

@@ -41,9 +41,12 @@
     <meta property="og:image" content="<%= conference()[:homepage] %><%= pathof('/assets/style/logo-gear/')[1..-1] %>">
 <% if @item.identifier == '/schedule/events/' %>
     <link href="https://cdn.datatables.net/2.2.2/css/dataTables.dataTables.min.css" rel="stylesheet" integrity="sha384-lidBvvi7oLJ2j9e3nFlBSXfo+giBJ9L7QnUdgjc3AvLiynS0HdKEEEZtvZ4izE46" crossorigin="anonymous">
+    <link href="https://cdn.datatables.net/fixedheader/4.0.1/css/fixedHeader.dataTables.min.css" rel="stylesheet" integrity="sha384-FidEgRBNslMjNcMkOFgR6bJnL/NNAjZYYob4PXzFLtqQpyiU7HYFjHfG2/OUWpvZ" crossorigin="anonymous">
 
     <script src="https://code.jquery.com/jquery-3.7.0.min.js" integrity="sha384-NXgwF8Kv9SSAr+jemKKcbvQsz+teULH/a5UNJvZc6kP47hZgl62M1vGnw6gHQhb1" crossorigin="anonymous"></script>
     <script src="https://cdn.datatables.net/2.2.2/js/dataTables.min.js" integrity="sha384-AenwROccLjIcbIsJuEZmrLlBzwrhvO94q+wm9RwETq4Kkqv9npFR2qbpdMhsehX3" crossorigin="anonymous"></script>
+    <script src="https://cdn.datatables.net/fixedheader/4.0.1/js/dataTables.fixedHeader.min.js" integrity="sha384-fLqXCJcrAdndivVvcmVV63KCTYYLJXHZwzlfgkRAiROtth7ZJaN3WJr+VaVe/asP" crossorigin="anonymous"></script>
+
 <% end %>
   </head>
   <body<%= @item.identifier =~ %r{^/schedule/([^/]+)/} ?  " class=\"schedule-#{$1}\"" : '' %>> 
@@ -192,6 +195,7 @@ <h3><%= column.keys.first.to_s %></h3>
       [3, 'asc'],
       [4, 'asc']
     ],
+    fixedHeader: true,
     paging:      false,
   });
 </script>