Include all photos as links in the RSS and Atom feeds, instead of just the thumbnail

- Move photo_thumbnail.html to photos/thumbnail.html
- Add a photos/list.html partial that returns a list of photos for the current
  page
- Use the template above everywhere we need a list of photos for the page

layouts/partials/photos/list.html

@@ -0,0 +1,9 @@
+{{ $thumbnailResourcesNames := slice "thumbnail" "Thumbnail" "thumbnail.jpg" "Thumbnail.jpg" }}
+{{ with index .Params "thumbnail" }}
+    {{ $thumbnailResourcesNames = $thumbnailResourcesNames | append . }}
+{{ end }}
+
+{{ $imageResources := .Resources.ByType "image" }}
+{{ $photos := where $imageResources "Name" "not in" $thumbnailResourcesNames }}
+
+{{ return $photos }}