Shift+mouse wheel up/down should result in a scroll

[darkhog]

It would improve the usability of the tool as you can currently only scroll via the UI buttons or via arrows. We cannot use regular mouse wheel as it has different uses, such as scaling arrangement tab, however we can use mouse wheel+some modifier key, such as shift to implement scrolling. Obviously the type of scroll (horizontal vs. vertical) should be relevant to the area currently under the cursor (arrangement roll should scroll horizontally, while instrument/pattern list, as well as pattern editor proper should scroll vertically, etc.)