Change the type key for delegate editors to int.

Change the type key for delegate editors to int.

Previous type of QVariant::Type does not allow for custom types.

While technically source incompatible I found no re-implementation
of this class in qttools or qt-creator (most likely to use it for
property editors). The virtual methods are not needed because
registerEditor is all the API that is really needed.

Task-number: QTBUG-1065

Change-Id: I2a9c578c444a80359416f2224a0ee03903bfe779
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Thorbjørn Lund Martsum <tmartsum@gmail.com>
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>