[Feature request, Jupyter Widget] Add event callbacks from Kepler widget back to Jupyter

**Is your feature request related to a problem? Please describe.**
I'm investigating approaches to prototype maps with Kepler.gl with Jupyter Notebook.
It's possible to pass data and config from Jupyter to Kepler widget, yet there's no possible way to interact backwards, from Kepler widget to Jupyter.

Is it actually a good idea to extend Kepler widget with any kind of callbacks (e.g. pass `onMapClick` event with coordinates to Jupyter in order to do some calculation on Jupyter side)?

**Describe the solution you'd like**
Add callbacks for Kepler events in a way as [standard Button does the callbacks](https://ipywidgets.readthedocs.io/en/latest/examples/Widget%20Events.html#Example)

**Describe alternatives you've considered**
It's possible to build a dedicated app on top of Kepler, but not sure if would be as fast as Jupyter to research any ideas based on map.
It's also possible to use just Leaflet plugin, yet it's required to implement own layers and filters on top of it.