School constructor
Constructeur de la classe School. Initialise les champs et génère un identifiant unique.
Implementation
School(this.name, this.country, this.content_type, this.available_slots,
this.b_slots, this.m_slots, this.specialization, this.graduation_level,
this.program, this.use_langage, this.req_lang_level,
this.academic_level) {
id = global_id;
remaining_slots = available_slots;
global_id++;
}