Added recognition for IE11, Opera 15+ and Maxthon, made Win 8.1 separate entry

These updates allow to recognize IE11, the new Opera with Blink engine (15+) and Maxthon.

Windows 8.1 is recognized as different OS from Windows 8, with abbreviation W81.

I also created a new UA test script including a number of modern browsers and renamed the previous version to UserAgentParser.test.oldbrowsers.php