message: Display correct logo on 404 page
diff: <header id="nav-header">
  <div id="nav-header-bg"></div>
  <div id="header-main" class="container">
  - <a href="/"><img id="logo" src="/img/logo-datenanfragen.svg"></a>
  + <a href="/" class="translatable">
  + <img id="logo" class="translatable-en" src="/img/logo-datarequests.svg">
  + <img id="logo" class="translatable-de" src="/img/logo-datenanfragen.svg">
  + <img id="logo" class="translatable-fr" src="/img/logo-demandetesdonnees.svg">
  + </a>
  <div class="clearfix"></div>
  </div>
  