prestashop: add javascript and/or css file to a theme

1. Add js and/or css files in /prestashop/themes/theme-name/js (or css).
2. Edit /prestashop/classes/controller/FrontController.php.
3. Add:

<?php
class FrontController extends FrontControllerCore
{
    public function setMedia()
    {
        parent::setMedia(); // CSS files
        Tools::addJS(_THEME_JS_DIR_.'myfile.js');
        Tools::addCSS(_THEME_CSS_DIR_.'myfile.css', 'all');
    }
}