Fixing bug where non-image types might break if app_config['original_date_visible'] is true

Not all media managers have the .get_original_date attribute, so of
course break.  This is fixed by making a new space where individual
media types can define this if they like.

This commit sponsored by Matthieu Dupont de Dinechin.  Thank you!

mediagoblin/templates/mediagoblin/media_displays/image.html

@@ -27,3 +27,20 @@
   {{ super() }}
   {% template_hook("image_sideinfo") %}
 {% endblock %}
+
+{% block mediagoblin_after_added_sidebar %}
+  {% if app_config['original_date_visible'] %}
+    {% set original_date = media.media_manager.get_original_date() %}
+
+    {% if original_date %}
+      <h3>{% trans %}Created{% endtrans %}</h3>
+
+      <p><span title="{{ original_date.strftime("%I:%M%p %Y-%m-%d") }}">
+        {%- trans formatted_time=timesince(original_date) -%}
+          {{ formatted_time }} ago
+        {%- endtrans -%}
+      </span></p>
+    {%- endif %}
+  {% endif %}
+{% endblock %}
+

mediagoblin/templates/mediagoblin/user_pages/media.html

@@ -154,19 +154,8 @@
         {%- endtrans -%}
     </span></p>
 
-    {% if app_config['original_date_visible'] %}
+    {% block mediagoblin_after_added_sidebar %}
-      {% set original_date = media.media_manager.get_original_date() %}
+    {% endblock %}
-
-      {% if original_date %}
-        <h3>{% trans %}Created{% endtrans %}</h3>
-
-        <p><span title="{{ original_date.strftime("%I:%M%p %Y-%m-%d") }}">
-          {%- trans formatted_time=timesince(original_date) -%}
-            {{ formatted_time }} ago
-          {%- endtrans -%}
-        </span></p>
-      {%- endif %}
-    {% endif %}
 
     {% if media.tags %}
       {% include "mediagoblin/utils/tags.html" %}