Fixes #2598, mousewheel event not firing on dom level 3 browsers

As described in #2598 I introduced a regression while updating the code to support the dom level 3 `wheel` event, since it wasn't add to the `Element.NativeEvents` map.
If Firefox is using `wheel` event, then `e.wheelDelta` is `undefined` and `event.detail` is `0` on both wheel directions. That is why I suggested (https://github.com/mootools/mootools-core/commit/1cd56d7e3fc4df43449b194c3ae8eb02b23d514d) the `e.deltaY` so the legacy `wheel` would have a value. I made a table with [related info here](https://docs.google.com/spreadsheets/d/1Gf41PhtPXZuwPGjh8Sc52s1JBd7VFPhpXtbbxLuLbjw/edit#gid=0).