Update header images

- Rename image.feature to header.image

_layouts/default.html

@@ -15,18 +15,17 @@ layout: compress
   {% include browser-upgrade.html %}
   {% include navigation.html %}
 
-  {% if page.image.feature %}
+  {% if page.header.image %}
     <div class="image-wrap">
     <img src=
-      {% if page.image.feature contains "http" %}
-        "{{ page.image.feature }}"
+      {% if page.header.image contains "http" %}
+        "{{ page.header.image }}"
       {% else %}
-        "{{ page.image.feature | prepend: "/images/" | prepend: absurl }}"
-        "{{ page.image.feature | prepend: absurl }}"
+        "{{ page.header.image | prepend: "/images/" | prepend: absurl }}"
       {% endif %}
       alt="{{ page.title }}">
-    {% if page.image.credit %}
-      <span class="image-credit">Photo Credit: <a href="{{ page.image.creditlink }}">{{ page.image.credit }}</a></span>
+    {% if page.header.credit %}
+      <span class="image-credit">Photo Credit: <a href="{{ page.header.credit.url }}">{{ page.header.credit.caption }}</a></span>
     {% endif %}
     </div><!-- /.image-wrap -->
   {% endif %}