Implement sort algorithm in olal

[MeierTobias]

To ensure that the reservation with the most seats is processed first, a sorting algorithm should be implemented. It's not necessary for the optimization logic but it increases the chance that all the group members are able to sit next to each other.
See TODO in olal.c

possible sort algorithms:
Merge sort: https://www.geeksforgeeks.org/merge-sort/
Counting sort: https://www.techiedelight.com/efficiently-sort-array-duplicated-values/