Add navigation bar

Closes: #89

templates/navbar.html

@@ -0,0 +1,29 @@
+{% macro navbar() %}
+
+{% set pages = [
+  {"endpoint": "index", "label": "Home" },
+  {"endpoint": "conference_list", "label": "Conference" },
+  {"endpoint": "travel_list", "label": "Travel" },
+  {"endpoint": "accommodation_list", "label": "Accommodation" },
+  {"endpoint": "gaps_page", "label": "Gaps" },
+] %}
+
+<nav class="navbar navbar-expand-lg bg-success" data-bs-theme="dark">
+  <div class="container-fluid">
+    <a class="navbar-brand" href="{{ url_for("index") }}">Agenda</a>
+    <button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
+      <span class="navbar-toggler-icon"></span>
+    </button>
+    <div class="collapse navbar-collapse" id="navbarSupportedContent">
+      <ul class="navbar-nav me-auto mb-2 mb-lg-0">
+        {% for page in pages %}
+        <li class="nav-item">
+          <a class="nav-link{% if request.endpoint == page.endpoint %} border border-white border-2 active{% endif %}" href="{{ url_for(page.endpoint) }}">{{ page.label }}</a>
+        </li>
+        {% endfor %}
+      </ul>
+    </div>
+  </div>
+</nav>
+
+{% endmacro %}