INT-3528 Use Collections min and max methods where appropriate

JIRA: https://jira.spring.io/browse/INT-3528

Use min and max methods instead of sorting an entire collection to get the minimum or maximum element.
I'd say that this `new SequenceNumberComparator()` should be pulled to the `final` property of the class, as it is in the `SequenceSizeReleaseStrategy`.

I see some other places where we can avoid similar inline `new Comparator()`, but I will adress them on merge