Move Curated pool updater to Danbooru.

* Move the Curated pool updater from Reportbooru to Danbooru.

* Change the process for selecting curated posts. Previously it was
  every post from the last week with at least three supervotes. This was
  flawed because it included both super-upvotes and super-downvotes. Now
  it's the top 100 posts from the last week, ordered from most super-upvoted
  to least.

config/danbooru_default_config.rb

@@ -41,6 +41,11 @@ module Danbooru
       ForumTopic.where(title: "Upload Feedback Thread").first
     end
 
+    # The ID of the "Curated" pool. If present, this pool will be updated daily with curated posts.
+    def curated_pool_id
+      nil
+    end
+
     def source_code_url
       "https://github.com/r888888888/danbooru"
     end