sys/shell: add CONFIG_NCGET_DEFAULT_DATA_DIR option
sys/shell: add CONFIG_NCGET_DEFAULT_DATA_DIR option

ant9000/RIOT,kYc0o/RIOT,miri64/RIOT,kYc0o/RIOT,kaspar030/RIOT,kaspar030/RIOT,kYc0o/RIOT,kYc0o/RIOT,jasonatran/RIOT,jasonatran/RIOT,ant9000/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,miri64/RIOT,RIOT-OS/RIOT,ant9000/RIOT,RIOT-OS/RIOT,miri64/RIOT,ant9000/RIOT,kYc0o/RIOT,miri64/RIOT,kaspar030/RIOT,ant9000/RIOT,jasonatran/RIOT,miri64/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,jasonatran/RIOT