Enable autolink extension on Pegdown
Various improvements to the way related items are rendered for keywords.
 - Keywords now have a proper description display
 - related item lists are always rendered with watched-item context, which
   means that we need to fetch watched items for almost every portal request.
   Issue #244 is a reminder that caching would be nice here.
 - Descriptions with links in them, and concepts where the name is actually
   a link, get auto-linkified.
 - Broader terms are shown in breadcrumbs but not narrower terms

Closes #243.