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

https://issues.apache.org/jira/browse/CB-6976

* Allow using new windows alias to work with old windows8 platform
* Allow using old windows8 alias to work with new windows universal apps
Looks like this makes it impossible to use whatever is in platforms/windows.
Both widows and windows8 platforms passed to the cli will refer to platforms/windows8
Is this the intent?