[feature]models-change+authentification+registration

Authentication and registration fully functional, merge and conflict resolved with Aichatou's code, statistic removed from the doctors' dashboard, PatientController created but not implemented (Aichatou's task), patient-dashboard template added, admin user not yet implemented but present in the list when registering (we'll see if we keep this one). We need to resolve the fact that one doctor can retrieve appointments from all the doctors and that we can access the medical records of all the patients, no matter who is connected, by changing the URL directly.