CB-6976 Add support for Windows Universal apps (Windows 8.1 and WP 8.1)

https://issues.apache.org/jira/browse/CB-6976

* Added new windows platform
* New platform can detect and correctly build both old Windows8 and new Windows project templates
* To have existing plugins working and for smooth transition added logic to re-use windows8 configuration settings (plugin.xml, config.xml).
* windows8 is now alias for windows. Both 'cordova some cmd windows8 and 'cordova some cmd windows' are equal