lektor opengraph support

model-page.ini

[model]
name = Page
label = {{ this.title }}

[fields.title]
label = Title
type = string

[fields.meta_title]
label = MetaData Title
type = string

[fields.meta_description]
label = MetaData Description
type = string

[fields.og_title]
label = OpenGraph Title
type = string

[fields.og_description]
label = OpenGraph Description
type = string

[fields.body]
label = Body
type = markdown

templates-page.html

{% extends "site_layout.html" %}
{% block title %}{{ this.title }}{% endblock %}
{% block meta_title %}{{ this.meta_title or this.title }}{% endblock %}
{% block meta_description %}{{ this.meta_description }}{% endblock %}
{% block og_title %}{{ this.og_title or this.meta_title or this.title }}{% endblock %}
{% block og_description %}{{ this.og_description or this.meta_description }}{% endblock %}
{% block body %}
  {{ this.body }}
{% endblock %}

templates-site_layout.html

<title>{% block title %}DEFAULT TITLE{% endblock %}</title>

    <meta name="title" content="{% block meta_title %}{% endblock %}"/>
    <meta name="description" content="{% block meta_description %}{% endblock %}"/>
    <meta name="author" content="AUTHOR"/>
    <link href="{{ this.url_path | url(external=True) }}" rel="canonical">

	<meta property="og:title" content="{% block og_title %}{% endblock %}" />
	<meta property="og:site_name" content="SITE NAME" />
	<meta property="og:url" content="{{ this.url_path | url(external=True) }}" />
	<meta property="og:description" content="{% block og_description %}{% endblock %}" />
	<meta property="og:type" content="website" />