make footer horizontally scrollable on small screens

The previous behavior was the footer became wider than the screen and the entire page width was increased.

evap/evaluation/templates/footer.html

@@ -6,7 +6,7 @@
         <div class="vote-bg-orange" style="width: 6%;"></div>
         <div class="vote-bg-red" style="width: 3%;"></div>
     </div>
-    <nav class="navbar navbar-expand">
+    <nav class="navbar navbar-expand overflow-x-scroll">
         <div class="collapse navbar-collapse justify-content-between">
             <ul class="navbar-nav justify-content-start">
                 <li class="nav-item my-auto">