Start implementing post info at bottom

Now, all posts show info about: author, updated date, tags.
However, styling is needed and also the tags part has to be fixed (we need to add a comma after every tag's name, excluding the last one)

partials/post-card-big.hbs

@@ -10,7 +10,7 @@
         <header class="mind-post-card-big_header">
             <p class="mind-post-card-big_meta"><span class="mind-post-card-big_tag">{{primary_tag.name}}</span>
                 •
-                <time class="post-date" datetime="{{date format='YYYY-MM-DD'}}">{{date format="DD MMMM YYYY"}}</time>
+                <time class="post-date" datetime="{{date published_at format='YYYY-MM-DD'}}">{{date published_at format="DD MMMM YYYY"}}</time>
             </p>
             <h3>{{title}}</h3>
         </header>