Fix #4016: Translated tags failing to find some tags.

* Normalize spaces to underscores when saving other names. Preserve case
  since case can be significant.

* Fix WikiPage#other_names_include to search case-insensitively (note:
  this prevents using the index).

* Fix sources to return the raw tags in `#tags` and the normalized tags
  in `#normalized_tags`. The normalized tags are the tags that will be
  matched against other names.

app/logical/sources/strategies/moebooru.rb

@@ -77,7 +77,7 @@ module Sources
 
       def tags
         api_response[:tags].to_s.split.map do |tag|
-          [tag.tr("_", " "), "https://#{site_name}/post?tags=#{CGI.escape(tag)}"]
+          [tag, "https://#{site_name}/post?tags=#{CGI.escape(tag)}"]
         end
       end