fluent connection for ButtonGadget

xybrid/ui/gadgets/buttongadget.h

@@ -34,6 +34,8 @@ namespace Xybrid::UI {
         inline ButtonGadget* setSize(qreal w, qreal h = 24) { size = {w, h}; update(); return this; }
         inline ButtonGadget* setText(const QString& t) { text = t; update(); return this;}
 
+        template<typename F> ButtonGadget* onClick(F f) { connect(this, &ButtonGadget::clicked, f); return this; }
+
     signals:
         void clicked();
     };