we need to test the apps

[floswald]

• we need to make sure that apps always run
• we need this: https://rstudio.github.io/shinytest/articles/shinytest.html
• I would like to keep everything within this one R package
• so i think we will have to move away from the apps inside the learnr tutorials and deploy each app as a standalone app.
• we can probably keep some tutorials
• but the majority of apps will be called with this strategy: https://deanattali.com/2015/04/21/r-package-shiny-app/