UI: Do not allow mouse wheel for volume slider

This commit fixes the issue of being able to scroll through the mixer
with the mouse wheel without modifying the volume slider.  This
functionality can be temporarily restored by holding a click on the
volume meter.

UI/slider-ignorewheel.hpp

@@ -5,11 +5,14 @@
 #include <QtCore/QObject>
 
 
+
+
 class SliderIgnoreScroll : public QSlider {
 	Q_OBJECT
 
 public:
 	SliderIgnoreScroll(QWidget *parent = nullptr);
+	SliderIgnoreScroll(Qt::Orientation orientation, QWidget *parent = nullptr);
 
 protected: