add_data for estimate_contrasts

[bwiernik]

It would be really nice if the plot method for estimate_contrasts had an argument to add the relevant raw data to the plot, ala:

library(modelbased)
library(see)
library(ggplot2)
model <- lm(Sepal.Width ~ Species, data = iris)
contrasts <- estimate_contrasts(model)
means <- estimate_means(model)

plot(contrasts, means) + geom_jitter2(aes(x = Species, y = Sepal.Width), data = iris, width = .2, height = 0, alpha = .2) + ylab("Sepal.Width")

^{Created on 2021-05-29 by the reprex package (v2.0.0)}

[DominiqueMakowski]

Since 'see' has been recently updated on CRAN, I'll submit this version of modelbased as is first, because I'd like to revise the plotting which will break the current see, so it's best if CRAN versions at working together