Prevent search engines from indexing admin pages

According to a google search I just did, it seems a lot of people have forgotten to add ``Disallow: /admin`` in their robots.txt (or forgot to add robots.txt) at all.

Adding this meta tag into the head of all admin pages should prevent any admin pages being indexed even if this was missed.

CHANGELOG.txt

@@ -6,6 +6,7 @@ Changelog
 
  * Added support for Django 2.1 (Ryan Verner, Matt Westcott)
  * Added 'scale' image filter (Oliver Wilkerson)
+ * Added meta tag to prevent search engines from indexing admin pages (Karl Hobley)
 
 
 2.2 (xx.xx.xxx) - IN DEVELOPMENT

docs/releases/2.3.rst

@@ -23,6 +23,7 @@ Other features
 ~~~~~~~~~~~~~~
 
  * Added 'scale' image filter (Oliver Wilkerson)
+ * Added meta tag to prevent search engines from indexing admin pages (Karl Hobley)
 
 
 Bug fixes

wagtail/admin/templates/wagtailadmin/skeleton.html

@@ -6,6 +6,7 @@
     <title>Wagtail - {% block titletag %}{% endblock %}</title>
     <meta name="description" content="" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <meta name="robots" content="noindex" />
 
     <script src="{% static 'wagtailadmin/js/vendor/modernizr-2.6.2.min.js' %}"></script>