Add asynchronous call to database.

See file 'asynchronous.ts'.

backend/templates/base_with_header.html

@@ -0,0 +1,16 @@
+{% extends "base.html" %}
+
+{% block body_container %}
+    <div class="header-container">
+        <h1><a href="/">~~ Recettes de cuisine ~~</a></h1>
+        {% match user %}
+        {% when Some with (user) %}
+            <div>{{ user.email }} / <a href="/signout" />Sign out</a></div>
+        {% when None %}
+            <div><a href="/signin" >Sign in</a> / <a href="/signup">Sign up</a></div>
+        {% endmatch %}
+    </div>
+    <div class="main-container">
+        {% block main_container %}{% endblock %}
+    </div>
+{% endblock %}