Feature Request: allow .phtml source files

Would it be possible to support template source files using the .phtml extension. Currently loco translate only parses .php and does not easily allow for modification.

In LocoAdmin changing the method to

public static function find_php( $dir ){
        $files = self::find( $dir, array('php', 'phtml') );
        return array_merge($files['php'], $files['phtml']);
    }

fixes it for me.

Properly an option to add arbitrary extensions from the backend would be even more flexible.

https://www.ads-software.com/plugins/loco-translate/