Engage with `ggtern` on approved stats/geoms and the print function

[benjaminleroy]

This issue focuses on compatibility with ggtern.

Goals:

• Create an issue ggtern requesting functionality like update_approved_layers (as seen in R/aaa.R) for package development extending off the ggtern. Maybe make a pull request for this as well for ggtern, and if successful -this would require a pull request to remove that function for EpiCompare and remove DESCRIPTION's dependence on ggtern (which makes us load in ggtern before our package).

• Create a pull request to ggtern, with our print.ggplot2 function as a solution for this issue.