refactor: split single header and meta components into partials

layouts/partials/single/post-meta/categories.html

@@ -0,0 +1,21 @@
+{{- /*
+  Displays the categories for an item.
+
+  @params categories  The item's categories.
+  */
+-}}
+
+
+<section
+  id="post-categories"
+  class="article-footer__categories"
+  aria-labelledby="post-categories-title"
+  itemprop="articleSection"
+>
+  <h3 id="post-categories-title">Categories</h3>
+  <ul>
+    {{- range .categories -}}
+      <li class="p-category"><a href="{{ .RelPermalink }}">{{ .LinkTitle | safeHTML }}</a></li>
+    {{- end -}}
+  </ul>
+</section>