Support for a new site setting: newuser_spam_host_threshold. If a new user posts a link

to the same host enough tiles, they will not be able to post the same link again.

Additionally, the site will flag all their previous posts with links as spam and they will
be instantly hidden via the auto hide workflow.

app/controllers/posts_controller.rb

@@ -39,8 +39,11 @@ class PostsController < ApplicationController
                                    meta_data: params[:meta_data],
                                    auto_close_days: params[:auto_close_days])
     post = post_creator.create
-
     if post_creator.errors.present?
+
+      # If the post was spam, flag all the user's posts as spam
+      current_user.flag_linked_posts_as_spam if post_creator.spam?
+
       render_json_error(post_creator)
     else
       post_serializer = PostSerializer.new(post, scope: guardian, root: false)