ui.gestures: increase mouse wheel scroll amount

[defaultxr]

Scrolling with the mouse wheel seems to scroll a lot less in Factor than it does in most other GUI programs. This change multiplies the scroll by 3 which makes it feel a lot closer to how scrolling works in other programs, requiring less mouse scrolling to move down a page.

[mrjbq7]

I wonder if an acceleration amount is more natural, so slow scrolling is a bit more like what we have and fast scrolling is a bit more like this PR