JS2 S3-prep to be broken down

**Background**
JS2 S3 Prep had some missing timing so I put all those exercises in one single timed exercise. Those have to be reviewed if suitable and then divided into separated into smaller ones.
There is also a glitch if you delete all the prep (optional).

**Acceptance criteria**
suitable exercises
appropriate timing

Responsible
@LaraHuzjan

Aproover
@kfklein15