post replacements: add "Tags" field to dialog box.

* Adds a "Tags" field to the post replacement dialog box. The given tags
  are added to the post after replacement.

* Prefills the Tags field with certain tags that usually need to be
  removed after replacement: replaceme, image_sample, jpeg_artifacts, etc.

config/danbooru_default_config.rb

@@ -386,6 +386,11 @@ module Danbooru
       true
     end
 
+    # Should return true if the given tag should be suggested for removal in the post replacement dialog box.
+    def remove_tag_after_replacement?(tag)
+      tag =~ /replaceme|.*_sample|resized|upscaled|downscaled|md5_mismatch|jpeg_artifacts/i
+    end
+
     def shared_dir_path
       "/var/www/danbooru2/shared"
     end