OSIS-5904 : refactor get_effective_classes
OSIS-5904 : refactor get_effective_classes

uclouvain/OSIS-Louvain,uclouvain/osis,uclouvain/osis,uclouvain/OSIS-Louvain,uclouvain/osis,uclouvain/osis,uclouvain/OSIS-Louvain