Add support for the standard wheel event.

[karthicks]

Currently, the FTScroller relies on the non-standard and deprecated DOMMouseScroll and mousewheel events, to handle scrolling. On certain recent versions of Firefox, the support for the former event appears to have been dropped, in favor of the standard wheel event.

In the pull request that will follow momentarily, a solution is proposed that was tested against the latest versions of Firefox, Opera and Chrome.