Move galleries to collection, generate map and slideshow on build, stop using loopdir plugin, update templates accordingly

_includes/gallery-list.html

@@ -0,0 +1,11 @@
+<div class="list-gallery">
+{% for p in site.pages %}
+    {% if p.layout == 'gallery-photo' and p.gallery == gallery %}
+    <span itemprop="image" itemscope itemtype="http://schema.org/Photograph">
+        <a href="/{{ site.baseurl }}/{{ p.url }}" itemprop="url">
+            <img alt="Photo: {{ p.title }}" height="200" src="{{ site.asset_prefix }}/gallery/{{ gallery }}/{{ p.name | remove:'.md' }}~200x200.jpg" title="{{ p.title }}" width="200" />
+        </a>
+    </span>
+    {% endif %}
+{% endfor %}
+</div>