consistently use organization name QtProject

This affects the location of the QSettings files or registry entries.
Other parts of Qt are using this organization name so it's good to
have all the settings in the same place.

Change-Id: Icbe61ab188b5561f935d959fdbaa885fbff4c3ec
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Reviewed-by: Martin Smith <martin.smith@digia.com>