fixed issue with visit numbers in statistics https://git-r3lab.uni.lu/NCER-PD/scheduling-system/-/issues/333\#note_46157

Avoid possibility to change the worker when adding holidays or extra availabilities. Changed the header

during save study is automatically injected into model

during save study is automatically injected into model

address, city, country, data_born, default_written_communication_language, email, first_name, languages, last_name, phone_number, phone_number_2, phone_number_3, postal_code removed from study_subject (all this information is stored in subject)

the code is fixed so unit test passes

when editing/adding appointment only locations and workers assigned to worker location are visible, workers are sorted alphabitecally,