implemented inverted timeline scroll axes

Timeline scrolls horizontally by default with a preference to disable that
functionality.

app/widget/timelinewidget/view/timelineview.cpp

@@ -27,6 +27,7 @@
 #include <QtMath>
 #include <QPen>
 
+#include "config/config.h"
 #include "common/flipmodifiers.h"
 #include "common/timecodefunctions.h"
 #include "core.h"
@@ -113,6 +114,21 @@ void TimelineView::mouseDoubleClickEvent(QMouseEvent *event)
   emit MouseDoubleClicked(&timeline_event);
 }
 
+void TimelineView::wheelEvent(QWheelEvent *event)
+{
+  if (Config::Current()["InvertTimelineScrollAxes"].toBool()) {
+    QWheelEvent e(event->pos(),
+                  event->delta(),
+                  event->buttons(),
+                  event->modifiers(),
+                  event->orientation() == Qt::Horizontal ? Qt::Vertical : Qt::Horizontal);
+
+    QGraphicsView::wheelEvent(&e);
+  } else {
+    QGraphicsView::wheelEvent(event);
+  }
+}
+
 void TimelineView::dragEnterEvent(QDragEnterEvent *event)
 {
   TimelineViewMouseEvent timeline_event(ScreenToCoordinate(event->pos()),