minor improvements:

- page titles
- favicon
- background logo

frontend/src/routes/document/List.svelte

@@ -76,6 +76,10 @@
     onMount(loadCompanies);
 </script>
 
+<svelte:head>
+    <title>Umbrella – {t('documents')}</title>
+</svelte:head>
+
 <fieldset>
     <legend>{selected_company ? t( 'docs_of_company',{company:selected_company.name}) : t('document_list')}</legend>
     {#if error}