Add curated posts page.

Add a curated posts page at /explore/posts/curated. Curated posts are
the most favorited posts by contributor-level users (users with
unlimited upload permissions).

Also add an order:curated tag using for use in regular searches.

app/views/static/site_map.html.erb

@@ -10,6 +10,7 @@
         <li><%= link_to("Upload", new_upload_path) %></li>
         <li><%= link_to("Upload Listing", uploads_path) %></li>
         <li><%= link_to("Popular", popular_explore_posts_path) %></li>
+        <li><%= link_to("Curated", curated_explore_posts_path) %></li>
         <li><%= link_to("Most Viewed", viewed_explore_posts_path) %></li>
         <li><%= link_to("Votes", post_votes_path) %></li>
         <% if CurrentUser.can_approve_posts? %>