Add piwik event tracker

Author: caismith-ch

templates/includes/feature_info.tx

@@ -19,7 +19,7 @@
     <ul class="list list-bullet">
       <li><a href="/company-name-availability" target="_blank">Company name availability checker<span class="visuallyhidden">Link opens in new window</span></a></li>
        % if $c.config.feature.alphabetical_search {
-          <li><a href="/alphabetical-search" target="_blank">Alphabetical company search<span class="visuallyhidden">Link opens in new window</span></a><sup class="label phase-tag">New</sup></li>
+          <li><a <% if $c.config.piwik.embed { %> onclick="javascript:_paq.push(['trackEvent', 'Other useful tools', 'Alphabetical company search']);"<% } %> href="/alphabetical-search" target="_blank">Alphabetical company search<span class="visuallyhidden">Link opens in new window</span></a><sup class="label phase-tag">New</sup></li>
        % }
     </ul>
 </div>