script.js for proper plugin file structure

[DokuWiki wants](https://www.dokuwiki.org/devel:plugin_file_structure#javascript) a script.js, but we want to keep nicolaszhao's original file structure for timeselect (e.g. for future updates), thankfully DokuWiki sports [a special include mechanism](https://www.dokuwiki.org/devel:javascript#include_syntax)