Add warning if an invalid scale is passed

[mdamien]

When an invalid scale is passed, it's silently ignored if it's invalid. This makes it painful to debug (did I use the right parameter ? does this chart support colorscales ?). So I propose to add a warning for invalid scales.

Of course, people still have to do Plotly.setPlotConfig({logging: true});

[etpinard]

Thanks very much for the PR!

Personally, I would prefer making sure the very-undocumented Plotly.validate catches all invalid colorscales which should already be the case.

[alexcjohnson]

@etpinard I seem to recall we talked at some point about having a config setting that runs Plotly.validate during supplyDefaults or something, kind of a debug mode - is there an issue for this? @mdamien is right of course that this kind of error is tough to catch, but that's true of every attribute really, they'll all silently ignore invalid input.

[etpinard]

I seem to recall we talked at some point about having a config setting that runs Plotly.validate during supplyDefaults or something, kind of a debug mode - is there an issue for this?

Here' it is ➡️ #1741