Create grid styling for related posts module

- Add default teaser image
- Disable image watch gulp task

_includes/archive-grid-single.html

@@ -0,0 +1,25 @@
+{% include base_path %}
+
+{% if post.header.teaser %}
+  {% capture teaser %}{{ post.header.teaser }}{% endcapture %}
+{% else %}
+  {% capture teaser %}{{ site.teaser }}{% endcapture %}
+{% endif %}
+
+<div class="grid__item">
+  <a href="{{ base_path }}{{ post.url }}">
+    <article class="archive__item" itemscope itemtype="http://schema.org/CreativeWork">
+      <div class="archive__item-teaser">
+        <img src=
+          {% if teaser contains "http" %}
+            "{{ teaser }}"
+          {% else %}
+            "{{ teaser | prepend: "/images/" | prepend: base_path }}"
+          {% endif %}
+          alt="{{ page.title }}">
+      </div>
+      <h2 class="archive__item-title" itemprop="headline">{% if post.id %}{{ post.title | markdownify | remove: "<p>" | remove: "</p>" }}{% else %}{{ post.title }}{% endif %}</h2>
+      {% if post.excerpt %}<p class="archive__item-excerpt" itemprop="description">{{ post.excerpt | markdownify | strip_html | truncate: 160 }}</p>{% endif %}
+    </article>
+  </a>
+</div>