Add link to base template, update 'egg' image

app/templates/base.html

@@ -30,7 +30,7 @@
 
     <nav class="navbar navbar-expand-lg bg-secondary fixed-top text-uppercase" id="mainNav">
         <div class="container">
-            <a class="navbar-brand js-scroll-trigger amiv-brand" >
+            <a class="navbar-brand js-scroll-trigger amiv-brand" href="/">
                 <span class="amiv-brand__amiv">AMIV Jubiläum</span>
                 <span class="amiv-brand__hyphen"> - </span>
                 <span class="amiv-brand__burger"></span>Burger Contest</span>