#111 Scroll with MMB even if items selected with hold-down LMB

[treteimer]

When you want to DND items in windows with more than one page of contents it takes a lot of time to go to the top or bottom and wait until the scrolling brings you to the right position. It'd speed up operations a very lot if scrolling with MMB was possible. Funnily, it is possible as long as you did not finish your selection and only in list mode but when you did you can not scroll anymore. In neither case you can in icon mode.