Add tooling for concept exercises

[ellnix]

Currently I have a couple things in mind:

• a generate command for creating concept exercises
• make the update command work with concept exercises (currently generate_exercise_files looks inside of exercises/practice)
• any helpful lints or checks I think of that configlet doesn't do (nothing specific so far)

Thought I'd open this issue first instead of just submitting a cold PR.

[senekor]

I think there are no "problem-specifications" for concept exercises, so an update command probably doesn't make sense.

[ellnix]

That's a really good point, they just happen to mostly be the same exercises as in problem-specifications, but we will have to maintain the tests ourselves.

[senekor]

Yeah. If there is a similar exercise in problem-specifications, the test cases there may serve as inspiration. But concept exercises are split in tasks and the tests need to map to these tasks. So it's not the same thing.

Btw I saw there's a a configlet command to add a concept exercise, not sure how much of the heavy lifting that already does.