Scrolling and zooming breaks down for tall graphs

[adamnovak]

When the graph has a lot of read coverage, like for the lancet graphs, scrolling and zooming starts to break down.

The graph is very tall so you want to zoom out, but when you hit the zooming limit you start scrolling the page instead, and then scrolling the wheel the other way to undo that goes back to zooming.

Also you can end up with a vertical scroll bar on the visualization itself, which doesn't seem appropriate and certainly can't work with a scroll wheel.

Either we have to stop the scroll wheel on the zoomable area scrolling, or we need to find another way to make this less confusing.

Another problem, possibly related, is that with a lot of reads you can have reads turning around outside the horizontal scrollable area.