Fix/improve cross browser wheel scrolling

Hi Guy,

I found an issue with a wheel scrolling code.
It would break on Firefox 30+ because the `scrollBy()` method didn't exist (it's an old DOM-0 method and I guess they removed it eventually).

I've now added some alternate code to fix this.

Could you merge this?

Thanks,

David

PS: I've also regenerated the dist js files; which shows that it was missed during the last code release.