use configured %contact_email% instead of hard-coded contact email

address on every page

templates/layout.html

@@ -29,7 +29,7 @@
       <div class="col-md-12">
         <hr />
         <div class="text-center footer" style="margin-bottom: 10px;">
-          <a href="%faq_url%">FAQ</a> · <a href="mailto:erzengel@lists.ccc.de"><span class="glyphicon glyphicon-envelope"></span> Contact</a> · <a href="https://github.com/engelsystem/engelsystem/issues">Bugs / Features</a> · <a href="https://github.com/engelsystem/engelsystem/">Development
+          <a href="%faq_url%">FAQ</a> · <a href="%contact_email%"><span class="glyphicon glyphicon-envelope"></span> Contact</a> · <a href="https://github.com/engelsystem/engelsystem/issues">Bugs / Features</a> · <a href="https://github.com/engelsystem/engelsystem/">Development
             Platform</a> · <a href="?p=credits">Credits</a>
         </div>
       </div>