Add support for config file in image directory

This config file will be loaded together with the images and defines the
passwords for login and some other parameters.

templates/index.html

@@ -7,6 +7,14 @@
         padding: 0.7rem;
         margin: 0;
     }
+    header {
+        font-size: 1.3rem;
+        padding: 1rem;
+        margin-bottom: 1rem;
+        background-color: #ebff7a;
+        border: 3px solid #b0cf00;
+        border-radius: 1rem;
+    }
     main {
         display: flex;
         flex-wrap: wrap;
@@ -42,10 +50,15 @@
 {% endblock head %}
 
 {% block main %}
+    {% if top_message %}
+    <header>
+        {{top_message}}
+    </header>
+    {% endif %}
     <main>
     {% for image in images %}
         <div style="aspect-ratio: {{image.width}} / {{image.height}}; flex-grow: {{10*image.width/image.height}};">
-        <img loading="lazy" src="/image/{{image.encrypted_name}}" alt="YOU SHALL NOT SAVE THIS IMAGE!" />
+        <img loading="lazy" src="/image/{{image.encrypted_name}}" alt="Could not load image" />
         </div>
     {% endfor %}
     </main>