Task#778 export user data

        Return all data concerning a user
        specify a user using --username=...
        Optionnaly you can specify a file to output with --file
        If not file specified, the filnemane will be export_[username].log
        The output file will be store on /tmp
        
        ./manage.py lms export_data_user --settings=fun.lms_sloop --username=anonymized1 [--file=toto.txt]
        [--host=127.0.0.1][--user_mongo=user_for_mongo][--pwd_mongo=password_for_mongo]