Issue 5445 - Add missing essential meta data to acceptableads.com

includes/meta.tmpl

 {#
  # This file is part of acceptableads.org.
  # Copyright (C) 2016 Eyeo GmbH
  #
  # acceptableads.org is free software: you can redistribute it and/or modify
  # it under the terms of the GNU General Public License as published by
  # the Free Software Foundation, either version 3 of the License, or
  # (at your option) any later version.
  #
  # acceptableads.org is distributed in the hope that it will be useful,
  # but WITHOUT ANY WARRANTY; without even the implied warranty of
  # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  # GNU General Public License for more details.
  #
  # You should have received a copy of the GNU General Public License
  # along with acceptableads.org.  If not, see <http://www.gnu.org/licenses/>.
  #}
 
 {# HTML5 essentials #}
 <meta charset="utf-8">
 <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
 <meta http-equiv="x-ua-compatible" content="ie=edge">
 
 {# HTML5 meta #}
 <title>{{ title | translate("page-title", "Page title") }}</title>
 <meta name="description" content="{{ description | translate('page-description', 'Page description') }}">
+<link rel="canonical" href="{{ get_canonical_url(page) }}" />
 
 {# http://ogp.me/ #}
 <meta property="og:image" content="{{ (og_image if og_image else meta.og_image) | translate('og-image', 'Open graph image')}}">
+<meta property="og:title" content="{{ title | translate("page-title") }}">
+<meta property="og:description" content="{{ description | translate("page-description") }}">
+<meta property="og:locale" content="{{ locale | to_og_locale }}">
+{% for alternate_locale in locales %}
+  {% if alternate_locale != locale %}
+    <meta property="og:locale:alternate" content="{{ alternate_locale | to_og_locale }}">
+  {% endif %}
+{% endfor %}
+<meta property="og:url" content="{{ get_canonical_url(page) }}">
 
 {# https://dev.twitter.com/cards/markup #}
 <meta name="twitter:card" content="{{ meta.twitter_card }}">
 <meta name="twitter:site" content="{{ meta.twitter_site }}">
 <meta name="twitter:creator" content="{{ meta.twitter_creator }}">
 <meta name="twitter:image" content="{{ (twitter_image if twitter_image else meta.twitter_image) | translate('twitter-image', 'Twitter image') }}">
 <meta name="twitter:image:alt" content="{{ (twitter_image_alt if twitter_image_alt else meta.twitter_image_alt) | translate('twitter-image-alt', 'Twitter image alternate text') }}">