Rewrite all SCTs according to new version of shellwhat

[filipsch]

Major refactor of SCTs …

• Bake in new version of shellwhat (and protowhat)
• Rewrite + (hopefully significantly) improve all SCTs accordingly.
  • Look at side effects of commands whenever possible to allow for more flexibility.
• Minor improvements to exercises and instructions here and there.

Closes #44 Closes #30 Closes #19 Closes #18 Closes #24

As you can see, I haven't changed too much about assignment text, instructions and those kinds of things, even though I think the course could use some love. Overall:

• Way too little information about how the exercises are set up!
• There is no narrative throughout the exercises. The setup is always different. This is confusing for students.
• The tone of speech is dry, and explanations are very minimalistic
• Instructions or the 'story telling' could be more interesting.
• There are a bunch of BulletConsoleExercise's in there with one bullet. If you switch this to simple ConsoleExercise, you mess up people's XP though, so I didnt' do it. (it goes from a parent exercise with a subexercise to a single exercise). I would not change this without consulting with the main/learn engineering teams.

Let me know if there are any questions.

[richierocks]

Main content changes

• ch1ex9: The new SCTs meant I had to teach git commit --amend so students who commited with the wrong message could fix what they'd done.
• ch2ex1: Rewrote the explanation of commits/trees/blobs so it relates more closely to the diagram.
• ch3: The new SCTs meant I had to introduce git reset in the same exercise as git add so students could undo any mistakes, and this had no knock-on changes throughout the rest of the chapter.
• ch5: I dropped any mention of file:// since it was very technical and only provides a minor performance benefit (https://stackoverflow.com/q/52259364/134830).
• various: I added a few comments on when the tasks would be performed in a data science workflow.