Rewrite all old-skool SCTs into sheetwhat SCTs

[filipsch]

Currently, both the feedback api and the new sheetwhat-app are used for SCTs, depending on the format SCT. We should get rid of the feedback api entirely in favor of the sheetwhat app, so we can clean things up (in the spreadsheets app and in the validator). See this doc for context.

• Spreadsheets basic (@vincentvankrunkelsven)
• Data analysis with spreadsheets (@vincentvankrunkelsven)
• Intermediate Spreadsheets for Data Science (@hermansje)
• Pivot tables (a CD or CQ, shouldn't be too much work)

This course can be safely used to experiment: https://spreadsheets.datacamp.com/courses/9