ui: Use a PNG favicon

frontend/ui/src/app.html

@@ -4,7 +4,6 @@
     <meta charset="utf-8">
     <meta name="viewport" content="width=device-width, initial-scale=1">
     <meta http-equiv="X-UA-Compatible" content="IE=edge">
-    <link rel="shortcut icon" type="image/x-icon" href="favicon.ico">
     <meta name="robots" content="all">
     <base href="/">
     %sveltekit.head%

frontend/ui/src/routes/__layout.svelte

@@ -148,6 +148,9 @@
     {#if $challengeInfo}
         <title>{$challengeInfo.title}</title>
         <meta name="author" content="{$challengeInfo.authors}">
+        {#if $challengeInfo.main_logo.length}
+            <link rel="icon" href="{$challengeInfo.main_logo[0].replace('$FILES$', '/files/')}">
+        {/if}
     {/if}
 </svelte:head>