Update get_js_urls and get_css_urls to return absolute URLs.

The `get_js_urls` and `get_css_urls` functions weren't returning full URLs that were suitable for downloading the assets because they weren't calling `_get_item_path` on the items they were listing out. This fixes that so that the URLs returned by the functions can be used to download the asset as they include the media URL.

Also fixes a few line length issues.