We should consider adding |ticks| to the wheel event.

There are many UX use cases where ticks are more appropriate than pixels, especially considering that pixel values vary from system-to-system (and can vary based on user preferences).

An example of when ticks are more appropriate is with a "digit-selector", a menu or a drop-down list. In each of these cases, a single tick should select the next element regardless of how many "pixels" are reported.

Issues:
What ticks value should be used for input devices that fake scrollwheel events (like a touchpad)?  Options are to simply use 0 ticks for these devices, come up with a method for generating fake ticks.

Do we need x, y and z ticks?