Change IRC to Slack

design/privateheader.php

           </li>
           <li id="nav_irc"<?=
             Format::add_class($PageID, ['chat'], 'active', true)?>>
-            <a href="chat.php">IRC</a>
+            <a href="https://biotorrents.slack.com" target="_blank">Slack</a>
           </li>
           <li id="nav_top10"<?=
             Format::add_class($PageID, ['top10'], 'active', true)?>>