First draft for `plot_moments` function (work-in-progress)

[hanneoberman]

How to scale the statistics to make this as informative as possible (e.g. variance vs SD). And should the imputed data be the imputed values only, or the statistics after pooling? I'm also considering plotting the between-imputation variability instead of the average statistics on the imputed data only.

imp <- mice::mice(mice::nhanes, print = FALSE)
ggmice:plot_moments(imp)