Optimize Open Graph metadata to HTML headers

[aschrijver]

Add sufficient Open Graph and other meta tags to the HTML header.

[aschrijver]

Most important Open Graph info is present, but needs to be further improved:

<meta name="description" content="Our global community of concerned people focuses on the rising harms of new technology, as it is radically transforming our world. And our mission is to change this trend.  To Re-align Technology to Humanity’s Best Interests.  — The Center for Humane Technology">
<meta property="og:type" content="website">
<meta property="og:locale" content="en_US">
<meta property="og:site_name" content="Humane Tech Community">
<meta property="og:title" content="Humane Tech Community">
<meta property="og:url" content="http://localhost:4000/">
<meta property="og:description" content="Our global community of concerned people focuses on the rising harms of new technology, as it is radically transforming our world. And our mission is to change this trend.  To Re-align Technology to Humanity’s Best Interests.  — The Center for Humane Technology">
<meta property="og:image" content="http://localhost:4000/assets/images/humane-tech-community-ogimage.png">

<script type="application/ld+json">
    {
      "@context": "http://schema.org",
      "@type": "Organization",
      "url": "http://localhost:4000/",
      "logo": "http://localhost:4000/assets/images/humane-tech-community-ogimage.png"
    }
</script>

<script type="application/ld+json">
    {
      "@context": "http://schema.org",
      "@type": "Person",
      "name": "Arnold Schrijver",
      "url": "http://localhost:4000/",
      "sameAs": null
    }
</script>

[aschrijver]

Does not work on WhatsApp yet, or it is a cache issue.
Looked at details here: https://stackoverflow.com/questions/25100917/showing-thumbnail-for-link-in-whatsapp-ogimage-meta-tag-doesnt-work#32154775

[aschrijver]

LinkedIn and Twitter previews do also not work properly. See #29