Add many functional/list-handling functions to nk_common.sh
Add many functional/list-handling functions to nk_common.sh

* Add: __pickle_arg(), __wrap_arg(), __wrap(), __check_arg(), __check(),
       __filter_arg(), __apply_arg(), __apply(), __pickle(), __file_writable(),
       __file_exists_tag()
* Improve: __map() - to handle lists

rowanthorpe/noc-kit