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/thumbnail.html

@@ -0,0 +1,25 @@
+{{- $thumbnailResource := .Page.Resources.GetMatch
+                            (index .Page.Params "thumbnail" | default "[tT]humbnail*")
+                        | default (index (.Page.Resources.ByType "image") 0) -}}
+
+{{- if not $thumbnailResource -}}
+  {{- errorf "No thumbnail available for %s" .Page.Permalink }}
+{{- end -}}
+
+{{ $orientation := partial "images/orientation_angle.html" $thumbnailResource }}
+
+{{ $targetWidth := 0 }}
+{{ if isset . "Width" }}{{ $targetWidth = .Width }}{{ else }}{{ $targetWidth = $thumbnailResource.Width }}{{ end }}
+{{ $targetHeight := 0 }}
+{{ if isset . "Height" }}{{ $targetHeight = .Height }}{{ else }}{{ $targetHeight = $thumbnailResource.Height }}{{ end }}
+
+{{ $thumbnail := false }}
+{{ if not (and (eq $orientation 0)
+               (eq $targetWidth $thumbnailResource.Width)
+               (eq $targetHeight $thumbnailResource.Height)) }}
+  {{ $thumbnail = $thumbnailResource.Fit (printf "%dx%d r%d" $targetWidth $targetHeight (sub 360 $orientation)) }}
+{{ else }}
+  {{ $thumbnail = $thumbnailResource }}
+{{ end }}
+
+{{ return $thumbnail }}