Put XMPP in list of master services

Renamed "chat" to "irc" for clarity.

services.php

@@ -1,6 +1,7 @@
 <?php
 $services = [
-    'chat' => ['fa' => 'comments-o', 'url' => '/wiki/irc'],
+    'irc' => ['fa' => 'comments-o', 'url' => '/wiki/irc'],
+    'xmpp' => ['fa' => 'fa-xmpp', 'url' => '/wiki/xmpp'],
     'cryptpad' => ['fa' => 'sticky-note', 'url' => 'https://pad.tildeverse.org'],
     'forum' => ['fa' => 'comment', 'url' => 'https://bbj.tildeverse.org'],
     'gitea' => ['fa' => 'code-fork', 'url' => 'https://tildegit.org/team'],