FEATURE: Add querystring value for Visible

Allow advanced functionality to only show visible topics on the latest, unread, new pages.

lib/topic_query.rb

@@ -288,6 +288,8 @@ class TopicQuery
           result = result.where('topics.closed')
         when 'archived'
           result = result.where('topics.archived')
+        when 'visible'
+          result = result.where('topics.visible')
         end
       end