Fix wagtailuserbar to assemble unicode properly as suggested by @spapas in 01646aafc8, and use textual dates

wagtail/wagtailadmin/templates/wagtailadmin/pages/_moderator_userbar.html

@@ -1,7 +1,7 @@
 {% load i18n %}
 <div class="wagtail-moderator-controls">
     <div class="message">
-        <p>{% blocktrans with title=revision.page.title submitted_by=revision.user.get_full_name|default:revision.user.username submitted_on=revision.created_at|date:"Y-m-d H:i" %}
+        <p>{% blocktrans with title=revision.page.title submitted_by=revision.user.get_full_name|default:revision.user.username submitted_on=revision.created_at|date:"d M Y H:i" %}
             Previewing '{{ title }}', submitted by {{ submitted_by }} on {{ submitted_on }}.
         {% endblocktrans %}</p>
     </div>

wagtail/wagtailadmin/templatetags/wagtailuserbar.py

@@ -8,10 +8,10 @@ register = template.Library()
 @register.simple_tag(takes_context=True)
 def wagtailuserbar(context, cssfile=None):
     try:
-        items = format_html_join('', '<li>{0}</li>', [(item,) for item in context['request'].userbar])
+        items = format_html_join(u'', u'<li>{0}</li>', [(item,) for item in context['request'].userbar])
         context.hasuserbar = True
         if not cssfile:
             cssfile = staticfiles_storage.url('wagtailadmin/css/wagtail-userbar.css')
-        return format_html('<link rel="stylesheet" href="//fonts.googleapis.com/css?family=Open+Sans:400" /><link rel="stylesheet" href="{0}" /><ul id="wagtail-userbar">{1}</ul>', cssfile, items)
+        return format_html(u'<link rel="stylesheet" href="//fonts.googleapis.com/css?family=Open+Sans:400" /><link rel="stylesheet" href="{0}" /><ul id="wagtail-userbar">{1}</ul>', cssfile, items)
     except AttributeError:
         return ''