Adapt to ggplot2 best practices

[lazappi]

https://ggplot2.tidyverse.org/dev/articles/ggplot2-in-packages.html

[llrs]

I recently saw your toot about updating clustree that linked to the https://github.com/lazappi/clustree/tree/version1 's branch.
I'm not sure if I'll have time, but I am starting to use it and I'll try to contribute to fix a couple of things if I can.

[lazappi]

Ok, cool. Be aware that that branch is incomplete and there is likely to be functionality that doesn't work well/at all. I did have a project board showing the progress but I think I lost it when GitHub migrated to the new projects so I can't tell you exactly where things were at 😿.