Infrastructure

thus far, oxt wasn't in the set of extensions that piwik considers a "download", so those were listed as page-actions.
Changed the tracking code to

<!-- Piwik -->
<script type="text/javascript">
  var _paq = _paq || [];
  _paq.push(['trackPageView']);
  _paq.push(['enableLinkTracking']);
  (function() {
    var u="//piwik.documentfoundation.org/";
    _paq.push(['setTrackerUrl', u+'piwik.php']);
    _paq.push(['setSiteId', 56]);
    _paq.push(['addDownloadExtensions', 'oxt']);
    var d=document, g=d.createElement('script'), s=d.getElementsByTagName('script')[0];
    g.type='text/javascript'; g.async=true; g.defer=true; g.src=u+'piwik.js'; s.parentNode.insertBefore(g,s);
  })();
</script>
<noscript><p><img src="//piwik.documentfoundation.org/piwik.php?idsite=56" style="border:0;" alt="" /></p></noscript>
<!-- End Piwik Code -->

Creating nice stats for the actual usage of extensions site is a little problematic, since plone doesn't use nice URLs, but uses query-parameters like e.g in
http://extensions.libreoffice.org/extension-center?getCategories=Writer_Extension
or
http://extensions.libreoffice.org/extension-center?b_start:int=20

so it needs some compilation of parameters to ignore...

Added the non-default "SearchableText" query parameter for in-site search and added the getCategories and getCompatibility parameters as limits for the search reports, that hopefully should help to get some halfway resonable results

Cloph to provide the CSS class and then re-assign it to Andreas for implementation

Lowering priority on this, as Andreas stated most extensions are downloaded from the Plone site, which can track data, and only a few extensions are hosted externally that need tracking