plot appearance

[roblanf]

change all plot themes to:

theme_minimal()

and change all colour schemes to default for discrete schemes. Our own scheme is a bit shit (currently we use: scale_color_viridis(discrete = TRUE, begin = 0.2, end = .8, option = "C"), but I honestly can't remember why and it looks a lot worse than just the default where you let ggplot do its thing for factors.

[danlwarren]

Viridis ramps are optimized for people with visual impairments, which was the reason for that choice. We can give options though.