Add Jekyll SEO Tag plugin

[george-gca]

It is a good idea to add Jekyll SEO Tag plugin. This will require minor changes in our code, but that needs to be properly verified.

An example run with Jekyll SEO Tag in our code generated the following extra data:

About page

<!-- Begin Jekyll SEO tag v2.8.0 -->
<title>about | blank</title>
<meta name="generator" content="Jekyll v4.3.2">
<meta property="og:title" content="about">
<meta property="og:locale" content="en_US">
<meta name="description" content="A simple, whitespace theme for academics. Based on *folio design.">
<meta property="og:description" content="A simple, whitespace theme for academics. Based on *folio design.">
<link rel="canonical" href="http://localhost:4000/al-folio/">
<meta property="og:url" content="http://localhost:4000/al-folio/">
<meta property="og:site_name" content="blank">
<meta property="og:type" content="website">
<meta name="twitter:card" content="summary">
<meta property="twitter:title" content="about">
<script type="application/ld+json">
{"@context":"https://schema.org",
 "@type":"WebSite",
 "description":"A simple, whitespace theme for academics. Based on *folio design.",
 "headline":"about",
 "name":"blank",
 "url":"http://localhost:4000/al-folio/"}</script>
<!-- End Jekyll SEO tag -->

Blog page

<!-- Begin Jekyll SEO tag v2.8.0 -->
<title>blog | blank</title>
<meta name="generator" content="Jekyll v4.3.2" />
<meta property="og:title" content="blog" />
<meta property="og:locale" content="en_US" />
<meta name="description" content="A simple, whitespace theme for academics. Based on *folio design." />
<meta property="og:description" content="A simple, whitespace theme for academics. Based on *folio design." />
<link rel="canonical" href="http://localhost:4000/al-folio/blog/" />
<meta property="og:url" content="http://localhost:4000/al-folio/blog/" />
<meta property="og:site_name" content="blank" />
<meta property="og:type" content="website" />
<link rel="next" href="http://localhost:4000/al-folio/blog/page/2/" />
<meta name="twitter:card" content="summary" />
<meta property="twitter:title" content="blog" />
<script type="application/ld+json">
{"@context":"https://schema.org",
 "@type":"WebPage",
 "description":"A simple, whitespace theme for academics. Based on *folio design.",
 "headline":"blog",
 "url":"http://localhost:4000/al-folio/blog/"}</script>
<!-- End Jekyll SEO tag -->

a post with code

<!-- Begin Jekyll SEO tag v2.8.0 -->
<title>a post with code | blank</title>
<meta name="generator" content="Jekyll v4.3.2">
<meta property="og:title" content="a post with code">
<meta property="og:locale" content="en_US">
<meta name="description" content="an example of a blog post with some code">
<meta property="og:description" content="an example of a blog post with some code">
<link rel="canonical" href="http://localhost:4000/al-folio/blog/2015/code/">
<meta property="og:url" content="http://localhost:4000/al-folio/blog/2015/code/">
<meta property="og:site_name" content="blank">
<meta property="og:type" content="article">
<meta property="article:published_time" content="2015-07-15T12:09:00-03:00">
<meta name="twitter:card" content="summary">
<meta property="twitter:title" content="a post with code">
<script type="application/ld+json">
{"@context":"https://schema.org",
 "@type":"BlogPosting",
 "dateModified":"2015-07-15T12:09:00-03:00",
 "datePublished":"2015-07-15T12:09:00-03:00",
 "description":"an example of a blog post with some code","headline":"a post with code",
 "mainEntityOfPage":{"@type":"WebPage","@id":"http://localhost:4000/al-folio/blog/2015/code/"},
 "url":"http://localhost:4000/al-folio/blog/2015/code/"}</script>
<!-- End Jekyll SEO tag -->

[george-gca]

After evaluating the metadata generated by Jekyll SEO Tag plugin and comparing it with our currently included metadata, I verified that basically we generate the same fields/values. The only difference was regarding blog posts, which I addressed in #1573.

Even though we could replace the current implementation by the plugin, I prefer to keep it that way because it enables some solutions like, for example, translating the metadata.