Reuse parent header image if page has none.

opentech/templates/base.html

@@ -68,8 +68,12 @@
         {% include 'includes/messages.html' %}
 
         {% block header %}
-            {% image page.header_image fill-2560x410 as header_image %}
-            <header class="header header--standard {% if page.header_image %}header--has-bg-image{% endif %} {% block header_modifier %}{% endblock %}" {% if page.header_image %}style="background-image:url('{{ header_image.url }}')"{% endif %}>
+            {% if page.header_image %}
+                {% image page.header_image fill-2560x410 as header_image %}
+            {% elif page.get_parent.header_image %}
+                {% image page.get_parent.header_image fill-2560x410 as header_image %}
+            {% endif %}
+            <header class="header header--standard {% if page.header_image %}header--has-bg-image{% endif %} {% block header_modifier %}{% endblock %}" {% if header_image %}style="background-image:url('{{ header_image.url }}')"{% endif %}>
 
                 {% block apply_button %}
                     {% include "includes/apply_button.html" %}