Add a <ul> of available translation for the page to the content header

Attempt to style it.

layouts/partials/content_header.html

@@ -5,6 +5,14 @@
     <time>{{ .Date | time.Format "January 2, 2006" }}</time>
   {{ end }}
 
+  {{ if gt (len .AllTranslations) 1 }}
+    <ul class=translations>
+    {{ range .AllTranslations }}
+      <li><a href="{{ .RelPermalink }}">{{ .Language.LanguageCode }}</a></li>
+    {{ end }}
+    </ul>
+  {{ end }}
+
   {{- if .Params.series -}}
     {{- $series := .GetTerms "series" -}}