make number of lines scrolled with mouse wheel configurable

src/screen.h

@@ -25,6 +25,7 @@
 #include "menu.h"
 #include "mpdpp.h"
 #include "helpers.h"
+#include "settings.h"
 #include "status.h"
 
 class BasicScreen
@@ -149,12 +150,12 @@ template <> inline void Screen<Scrollpad>::MouseButtonPressed(MEVENT me)
 {
 	if (me.bstate & BUTTON2_PRESSED)
 	{
-		for (size_t i = 0; i < 2; ++i)
+		for (size_t i = 0; i < Config.lines_scrolled; ++i)
 			Scroll(wDown);
 	}
 	else if (me.bstate & BUTTON4_PRESSED)
 	{
-		for (size_t i = 0; i < 2; ++i)
+		for (size_t i = 0; i < Config.lines_scrolled; ++i)
 			Scroll(wUp);
 	}
 }