Add ability to specify custom HTTP response code along with redirect header

Normally HTTP response code 302 (Found) is sent, when "kApplication::Redirect" method is called. However there are cases (like site migration to another software), when there is need to sent other header, like 301 (Moved Permanently).

I propose to add "response_code" parameter to url building process, to be processed by "kApplication::Redirect" method only.