swirl 2.5

[seankross]

• [ ] Add badges
• [ ] Add "viewer pane" questions
• [x] Integrate versions of testthat beyond 0.11.0
• [x] Fix file.edit() RStudio issue
• [ ] Add swirl_is_fun to swirl_options().
• [ ] Assign user agent in httr calls.
• [ ] Remove zip_course()
• [ ] Document the fact that install_course_github(multi = TRUE)` is for internal use only.
• [ ] Add number of steps remaining #589

[seankross]

Troublesome questions:

- Class: text_question
  Output: "What are the genotypes you can have and have blood type A."
  CorrectAnswer: "AA AO"
  AnswerTests: any_of_exprs("AA AO","AO AA")
  Hint: hint

And multiple right answers for multiple choice questions.

[cansavvy]

Based on the check marks being unchecked and this issue being closed, it looks like this version update wasn't complete, but we should figure out if there's any nuggets of wisdom for the redesign that we should pull out of this issue.