evaluation_metrics_plot fails when IRA fields are in the input EvaluationRow for multiclass result

[alexmchan]

Currently, if votes is not provided to Lighthouse.evaluation_metrics_row, it outputs a row with per_class_IRA_kappas and multiclass_IRA_kappas fields defined as missing. If this is a multiclass result, then passing in such a row to evaluation_metrics_plot fails because it doesn't expect these fields to exist when not dealing with multi-rater metrics.

For example, for a 5 class EvaluationRow, it throws:

ERROR: DimensionMismatch("arrays could not be broadcast to a common size; got a dimension with lengths 12 and 8")

[hannahilea]

oh geez. this will be an easy fix---I can make it for you asap, @alexmchan, unless you're already on it?

[hannahilea]

yet another reason that it will be exciting to do #71---plots shouldn't ask for more than they truly need/expect to plot. none of this evaluation_metrics_plot behemoth nonsense.

[alexmchan]

I'm already mostly through this one. Thanks for the offer though!