feat: Added Unified file system / default layout mounts.

defaults/layouts/section_index.html

@@ -0,0 +1,19 @@
+{{<base}}
+{{$content}}
+<main>
+  <h1>{{page_title}}</h1>
+  {{&body}}
+  {{#year_sections}}
+  <section>
+    <h2>{{year}}</h2>
+    <ul>
+      {{#posts}} <li><a href="{{permalink}}">{{&title}}</a><span>{{#date_iso}}<time
+            datetime="{{date_iso}}">{{date_display}}</time>{{/date_iso}}</span>
+      </li>
+      {{/posts}}
+    </ul>
+  </section>
+  {{/year_sections}}
+</main>
+{{/content}}
+{{/base}}