WIP Add script for creating drawables (png files shown in the app)

[atorch]

• Work in progress: add script for creating drawables (the .png files in res/drawable-hdpi)
  • TODO Make sure it runs, create args so that drawables can be created in German, Spanish, and other languages with translations -- that could help with https://github.com/atorch/probability_puzzles/issues/11
  • TODO I could look into creating a simple Docker container so that everyone can run the R drawables script with the same packages installed, same version of R, etc
• Other misc changes (added detail in some puzzle hints)