Add gallery, about and error pages

site/templates/gallery.twig

@@ -0,0 +1,29 @@
+{% extends "base.twig" %}
+
+{% block main %}
+    <main>
+
+        <section class="gallery-section">
+
+            <article class="gallery">
+                <h2 class="gallery__title">{{ page.title }}</h2>
+                {% if page.text.isNotEmpty %}
+                    <div class="gallery__introduction">{{ page.text.kirbytext|raw }}</div>
+                {% endif %}
+                <div class="gallery__artworks">
+                    {% for file in page.files %}
+                        {% if file.type == 'image' %}
+                            <figure class="gallery__image">
+                                <img src="{{ file.url }}" srcset="{{ file.srcset() }}" alt="{{ file.alt_text }}">
+                                <figcaption>{{ file.caption }}</figcaption>
+                            </figure>
+                        {% elseif file.type == 'video' %}
+                        {% endif %}
+                    {% endfor %}
+                </div>
+            </article>
+
+        </section>
+
+    </main>
+{% endblock %}