Finished second stage of the scrollbar implementation and added scrolling with...

Finished second stage of the scrollbar implementation and added scrolling with middle click. All scrollbars are now operational and to the best of my knowledge accurate. The only things remaining are: getscroll needs to be called on deselect to recalculate when the handles are erased on objects that have them (we should get rid of these and focus on bboxes instead), responding to maximizing and restoring, and addressing a weird bug where in 0.46.2 patches are saved with larger window sizes under certain conditions.