Add message flashing

src/lib/pug/base.pug

@@ -11,6 +11,7 @@ html(lang="en")
       include ./navigation
 
     .container.floating-container
+      include ./message-flash.html
       block content
 
     block footer

src/lib/pug/message-flash.html

@@ -0,0 +1,12 @@
+{% with messages = get_flashed_messages(with_categories=true) %}
+  {% if messages %}
+    {% for category, message in messages %}
+      <div class="alert alert-{{ category }} alert-dismissible fade show" role="alert">
+        {{ message }}
+        <button type="button" class="close" data-dismiss="alert" aria-label="Close">
+          <span aria-hidden="true">&times;</span>
+        </button>
+      </div>
+    {% endfor %}
+  {% endif %}
+{% endwith %}