[OSIS-3527] fetch requirement and allocation acronym from annotate
[OSIS-3527] fetch requirement and allocation acronym from annotate

Performance issue. The learning unit serializer generated two
queries for each learning unit year to fetch the requirement and
the allocation entity. Now the queryset used by the serializer
must have those data already fetched via annotation.

	modified:   learning_unit/api/serializers/learning_unit.py

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