[OSIS-3527] init cities and campus choices via value_list
[OSIS-3527] init cities and campus choices via value_list

	modified:   base/forms/learning_unit/search/external.py

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