auto-fill the .txt and .yaml files in the plugin tree during install_plugin.py script

Rather than requiring plugin writers to manually list the import-style path to files containing e.g. recipe modules or LMVis plugins, etc., would probably be OK if we assumed any file in e.g. `recipe_modules` directory should have an entry in the config tree and take care of that for everyone during the config-tree copy in `install_plugin.py`.