[C2] Export and Edit user by CSV and import classes should be with file with "," and no more with ";"

The import users by csv file functionnality has been modified to accept file with "," and nor more with ";"
The Export users (main/admin/user_export.php) and Edit users by csv (main/admin/user_update_import.php) and the class import (main/admin/usergroup_import.php) should also use "," instead of ";"