add possibility to set the onEnd callback  inside bounceOnAddOptions

With these changes, the onEnd callback can be set in the bounceOnAddOptions
```
L.marker([48.85, 2.35], { bounceOnAdd: true, bounceOnAddOptions: {duration: 500, height: 100, onEnd:callback} }).addTo(map);
```
or in the options of the bounce function:
```
marker.bounce({duration: 500, height: 100, onEnd:callback});
```