Free click in cartesian graphs

[nmalyschkin]

Hey!

I could really use a feature, that allows free click events in cartesian graphs. Currently click events are bound to points in data sets. This should be fairly easy to implement.

To make this a non-breaking feature, I propose to leave the plotly-click event as it is and add a new event called plotly-freeclick.

If there already is a feature for this, please point me in the right direction.
If there are reasons against such a feature, please tell me.

I offer myself to implement this feature.

[etpinard]

Thanks for posting!

This is a duplicate of #2696