generate events for plotly_log, plotly_warn, plotly_error

[nicolaskruchten]

From #4098 (comment)

It would be really helpful for the Dash user to be able to get warnings in the debug tools, especially for stuff like hierarchy problems in sunburst/treemap

[etpinard]

After #4555, this one should be fairly easy.

After #4555, the methods in the loggers.js module will have access to gd, which could then be used to call gd.emit with the correct arguments.