Fix broken wheel zoom in Firefox

@damianavila, @kdodia, @tabchas  could use windows, linux testing testing. Works on safari, chrome, and firefox on OSX. 
I have tried on multiple occasions, and it has not worked for me. The callback is called but `delta` is undefined. I just tried again, to summarize the change:
```

define [
  "jquery_mousewheel"
], (mousewheel) ->
``` 
at the top, then for the callback:
```
    @plotview.canvas_view.canvas_wrapper.mousewheel(
        (e, delta) =>
          if @tool_active or (not @eventSink.active and e.shiftKey)
            set_bokehXY(e)
            e.delta = delta
            eventSink.trigger("#{toolName}:zoom", e)
            e.preventDefault()
            e.stopPropagation()
      )
```
The fact that the callback is called with the jquery-mousewheel callback helper makes me think that jquery-mousewheel is getting required correctly. If you have any suggestions they are welcome.