Change SpinBoxDelegate example to be consistent with QItemEditorFactory

When QItemEditorFactory creates spinbox widgets for integer values and double values, it disables the frame for the widgets. However, spinboxdelegate creates a spinbox with a frame. It is not obvious that one needs to perform setFrame(false) on the delegate widget in order to reproduce the same appearance.

A suggestion would be to add editor->setFrame(false) to line 66 of delegate.cpp in examples/itemviews/spinboxdelegate. This way the appearance is consistent with the default spinboxes created by QItemEditorFactory.

The appearance without a frame is much nicer with the item views in particular.