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/logical/post_query_builder.rb

@@ -596,6 +596,16 @@ class PostQueryBuilder
     when "rank"
       relation = relation.order(Arel.sql("log(3, posts.score) + (extract(epoch from posts.created_at) - extract(epoch from timestamp '2005-05-24')) / 35000 DESC"))
 
+    when "curated"
+      contributors = User.bit_prefs_match(:can_upload_free, true)
+
+      relation = relation
+        .joins(:favorites)
+        .where(favorites: { user: contributors })
+        .group("posts.id")
+        .select("posts.*, COUNT(*) AS contributor_fav_count")
+        .order("contributor_fav_count DESC, posts.fav_count DESC, posts.id DESC")
+
     when "custom"
       if q[:post_id].present? && q[:post_id][0] == :in
         relation = relation.find_ordered(q[:post_id][1])