Add option to switch scroll behavior

An option to have the mouse wheel scroll vertically by default and horizontally when holding shift instead of the opposite. The reason I would like this:

1. Most other programs do it this way so I'm used to it
2. I use Kdenlive and Ardour simultaneously for precise sound synchronization and they have an opposite scroll behavior, so I almost always mix up vertical and horizontal scrolling which is quite frustrating.

I understand that editing a video is 90% horizontal scrolling but I would like to be able to switch the key binding anyway.

Such an option would probably belong in Settings > Configure Kdenlive > Timeline, as a checkbox.