QNX: new signals for foreign windows creation/closing

Implement the foreignWindowCreated and foreignWindow closed signals, emitted when foreign windows are created and closed, respectively.

Change-Id: I72dd5380e6061f191eb8362fda5dd8fb8e9ed06b
Reviewed-by: Thomas McGuire <thomas.mcguire@kdab.com>
Reviewed-by: Kevin Krammer <kevin.krammer@kdab.com>
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>