Add Matomo snippet for analytics

Available on https://webanalytics.web.cern.ch/

Will eventually be added to the new web services portal as it is for EOS websites

theme/partials/header.html

@@ -123,3 +123,19 @@
 
   </nav>
 </header>
+
+<!-- Matomo -->
+<script type="text/javascript">
+  var _paq = window._paq = window._paq || [];
+  /* tracker methods like "setCustomDimension" should be called before "trackPageView" */
+  _paq.push(['trackPageView']);
+  _paq.push(['enableLinkTracking']);
+  (function() {
+    var u="https://webanalytics.web.cern.ch/";
+    _paq.push(['setTrackerUrl', u+'matomo.php']);
+    _paq.push(['setSiteId', '99']);
+    var d=document, g=d.createElement('script'), s=d.getElementsByTagName('script')[0];
+    g.type='text/javascript'; g.async=true; g.src=u+'matomo.js'; s.parentNode.insertBefore(g,s);
+  })();
+</script>
+<!-- End Matomo Code -->