Checking for updates using xml response

For some time already CH used ini file placed on the copyhandler.com to get update information.
That format is problematic in conveying extended information like changelog or additional user-facing text. Also processing ini files using php is not as straightforward as xml files.

Need to change the server-side storage format for update information from ini to xml (ini need to stay for backward compatibility with pre-1.40).

Also, to limit transferred data, CH client need to send some data to the server (like OS, CH version, language).