plotly_click event hidden by default click event

In syncplot.js there are handlers defined for `'plotly_click'` and `click`, both writing to `model[prefix + '_click']`. Since the normal `click` handler runs later it overwrites the plotly event data with solely the cursor position.

Either the default handler shouldn't be called after the plotly handler or they should write to different variables.

Start in syncplot.js and inspect the 'plotly_click' and click handlers that both write to model[prefix + '_click']. Reproduce the event ordering, then ensure the plotly event data is not overwritten by the default click handler, or that the handlers use separate variables; done means plotly_click retains its event data.

Written by the indexing model from the issue text.