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/photos/single.html

@@ -3,13 +3,11 @@
 {{ end }}
 
 {{ define "main" }}
-{{- $photos := where (.Resources.ByType "image")
-               "Name" "not in" (slice "thumbnail" "Thumbnail" "thumbnail.jpg" "Thumbnail.jpg") -}}
-
 {{- if .Title -}}
   {{ partial "content_header.html" . }}
 {{- end -}}
 
+{{- $photos := partial "photos/list.html" . -}}
 {{ if eq (len $photos) 0 }}
   {{ errorf "Missing photo from photos page %q" .Path }}
 {{ end }}