Mousewheel support

The attached patch adds basic mousewheel support.

It also removes some unnecessary trailing whitespace from the edited files (this was done automatically by my editor).

I almost went with an update hook to back-fill the new config parameter, but seeing no prior update hooks / pattern of this in the module, I decided instead to just handle the situation in the form via a null coalescing operator.

Thanks for this one too, it is included in the latest 2.0.x-dev version. See also here.