BlackBerry 10 specific widget style as a style plugin

- upstreaming the implementation of a BlackBerry 10 specific widget style
- modfied to be integrated as a style plugin being a part of the QtBase
- according docs are provided in QtDocs in another commit
- attributing the excellent work at KDAB who was the original developer

Change-Id: I57c548f6ec4cf02f125ee216f1ce1b764f29e8bb
Reviewed-by: Bernd Weimer <bweimer@blackberry.com>
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>