I have the same issue! i add the folder picklist on my own theme and add the function require_once…

c:\frutabox\wp-content\themes\frutabox\picklist\picklist.php

////functions

require_once (picklist/piklist.php);
the classes are loaded, and i can see the the picklist demos. But, the images & js path are with path of plugin_url.

i dont have the plugin folder picklist, this is necessary?