add n_clicks to cellClicked

[AnnMarieW]

fixes #17

Added n_clicks data so setProps would update the data when the same cell is clicked on.

[BSd3v]

@alexcjohnson, my thoughts are we should use a timestamp instead of n_clicks.

• n_clicks is an extra state, though small, to keep track of
• a timestamp may be useful as some point in time for gauging an user's level of interaction?

[alexcjohnson]

Ooh yeah I like the timestamp idea. As we go along we might end up adding other timestamps as well, and there may be use cases where you can see which is the latest timestamp across different classes of actions, which wouldn't be possible with n_clicks. Also n_clicks itself is ambiguous, does it mean number of clicks on this cell? on any cell? for this event (ie 2 would be a doubleclick)? We could document but if we use timestamp there's no need.

[alexcjohnson]

💃 Excellent!