SpinSlider and ScrollSpinBox read-only support

PIVariantEdit - support for read-only for all types
PIValueTreeEdit - drop Parent grouping, default now Groups, full grouping control, global read-only support, fix new label error

libs/piqt_utils/pivariant_edit_widgets.h

@@ -78,6 +78,8 @@ public:
 	PIVariant value() const override { return widget->isChecked(); }
 
 private:
+	void applyAttributes(const PIVariantMap & a) override;
+
 	QCheckBox * widget;
 };