Add schema.org customizations to dataset page

Adds schema.org customizations to dataset info detail page, which should
fix issues with Google Dataset Search.

ckanext/ioos_theme/templates/package/read_base.html

@@ -22,6 +22,13 @@
   {{ h.build_nav_icon('dataset_activity', _('Activity Stream'), id=pkg.name) }}
 {% endblock %}
 
+{% block structured_data %}
+  <script type="application/ld+json">
+  {{ h.structured_data(pkg.id,
+                       ["schemaorg","euro_dcat_ap","ioos_dcat"])|safe }}
+  </script>
+{% endblock %}
+
 {% block primary_content_inner %}
     {% block package_revision_info %}
       {% if c.revision_date %}