Add Matomo tracking

[egpbos]

Following up on the discussion in #161, instead of Google Analytics, we should add Matomo tracking to the Guide. We also use Matomo for the corporate site and for the research software directory.

Veronica referred me to @ewan-escience who was able to give me an account on the RSD Matomo server. To enable Matomo tracking, we need to add a small piece of code in the rendered pages.

However, if we want to track, which uses cookies, we also need a cookie banner. So, two todo items in this issue:

• Figure out how to get a cookie wall and implement it. We could perhaps take inspiration from the RSD.
• Activate tracking, using the tracking code below (I'll update it if it becomes out of date, depending on fast someone will pick up this issue).

<!-- Matomo -->
<script>
  var _paq = window._paq = window._paq || [];
  /* tracker methods like "setCustomDimension" should be called before "trackPageView" */
  _paq.push(['trackPageView']);
  _paq.push(['enableLinkTracking']);
  (function() {
    var u="//matomo.research.software/";
    _paq.push(['setTrackerUrl', u+'matomo.php']);
    _paq.push(['setSiteId', '5']);
    var d=document, g=d.createElement('script'), s=d.getElementsByTagName('script')[0];
    g.async=true; g.src=u+'matomo.js'; s.parentNode.insertBefore(g,s);
  })();
</script>
<!-- End Matomo Code -->

[ewan-escience]

Related to tracking, and in the light of #161, can the data-ga="UA-55088238-8" code and the plugin ga.min.js be removed?`