Implement more image resizing, fix responsiveness

- Two new image sizes have been added: xl and xxl.
- Image resizing has been implemented in featured images.
- Some elements were not responsive, such as the link preview and code block.

partials/post-card-small.hbs

@@ -0,0 +1,25 @@
+{{!-- Gest the 3 most recent related posts --}}
+{{#get "posts" limit="3" filter="id:-{{post.id}}+tags:[{{post.tags}}]" include="tags" as |related|}}
+    <h4>Similar posts</h4>
+    {{#foreach related}}
+        <article class="{{post_class}}">
+            <a class="mind-post-card-sidebar_main" href="{{url}}">
+
+                {{#if feature_image}}
+                    <img class="mind-post-card-sidebar_feature-image" src="{{img_url feature_image size="s"}}"
+                         alt="Feature Image"/>
+                {{/if}}
+                <header class="mind-post-card-sidebar_header">
+                    <p class="mind-post-card-sidebar_meta"><span
+                            class="mind-post-card-sidebar_tag">{{primary_tag.name}}</span> •
+                        <time class="post-date" datetime="{{date format='YYYY-MM-DD'}}">{{date
+                                format="DD MMMM YYYY"}}</time>
+                    </p>
+                    <h5>{{title}}</h5>
+                </header>
+            </a>
+        </article>
+    {{/foreach}}
+{{else}}
+    <h4>No related posts</h4>
+{{/get}}