Blackberry: Fix crash when opening file dialog without parent.

Blackberry: Fix crash when opening file dialog without parent.

If parent is null, we now use qqnxintegration->primaryScreen()

This simplifies ctors of QQnxTheme and QQnxFileDialogHelper which now
receive a QQnxIntegration pointer instead of receiving a font database
and a bps event filter.

Change-Id: I3b1ed4d99f738b980a4f19a98618341a14e0c222
Reviewed-by: Kevin Krammer <kevin.krammer@kdab.com>
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>
Reviewed-by: Thomas McGuire <thomas.mcguire@kdab.com>