refactoring qad widgets part 2

c++ cast, nullptr, forward declaration, agregate ui, connect to member functions, order and clear includes

libs/widgets/image_view.h

@@ -52,7 +52,7 @@ signals:
 	void clicked(QPointF, Qt::MouseButtons);
 
 private:
-	void mouseDoubleClickEvent(QMouseEvent * e) override;
+	void mouseDoubleClickEvent(QMouseEvent *) override;
 	void mousePressEvent(QMouseEvent * e) override;
 	void wheelEvent(QWheelEvent * e) override;
 	bool eventFilter(QObject * o, QEvent * e) override;