Resolve "Implement some heap bubbling"

Closes #79 (closed)

This exercise is inspired by an old exam of ADS (CS edition): https://weblab.tudelft.nl/ti1315/2018-2019/assignment/21213/view

@yangelova Can you review this one for me? 🙂

@MrHug Additionally, I would like to ask you to what extent I should explain this exercise. Have they already seen heaps that are represented using a List, or should the exercise explain this?