This patch adds the WEB_SERVER_CONTENT_LANGUAGE parameter so the user can specify
the language used by the device during Description and Presentation steps of UPnP
through the HTTP CONTENT-LANGUAGE header.
By default, the WEB_SERVER_CONTENT_LANGUAGE is an empty string so no
CONTENT-LANGUAGE is added.
(cherry picked from commit 2fcbe6df52265576ad6bfc902541612ca89f30d4)