Show flash messages on event list.

templates/flash_messages.html

@@ -0,0 +1,12 @@
+{% with messages = get_flashed_messages() %}
+{% if messages %}
+<div class="container-fluid mt-2">
+  {% for message in messages %}
+  <div class="alert alert-success alert-dismissible fade show" role="alert">
+    {{ message }}
+    <button type="button" class="btn-close" data-bs-dismiss="alert" aria-label="Close"></button>
+  </div>
+  {% endfor %}
+</div>
+{% endif %}
+{% endwith %}