Some type constraints in methods using `jfxe.EventHandler` arguments have incorrect variance

For instance, in `Node` we have:

``` scala
def onRotate_=(v: jfxe.EventHandler[jfxsi.RotateEvent])
```

instead of 

``` scala
def onRotate_=(v: jfxe.EventHandler[_ >:jfxsi.RotateEvent])
```
