Scrolling sideways should scroll the matrix sideways

[Robert Leach]

Many mice allow you to scroll horizontally. Making that do a zoom instead seems a bit unintuitive and forces the user to scroll horizontally by clicking and dragging the scroll bar. I have submitted other feature requests to address zooming which should address the loss of zooming made by this change.

[Robert Leach]

Changed shift-scroll to scroll horizontally since magic mice and other mice with horizontal-scroll capability come through as if the shift was down (even though it's not) and switched zoom-scrolling to happen when alt/option is down.