[Paypal rest] updated payment factory.

```php
$config['options.required'] = array('client_id', 'client_secret', 'config_path');
if(!defined('PP_CONFIG_PATH')) {
    define('PP_CONFIG_PATH', $config['config_path']);
} else if (PP_CONFIG_PATH == $config['config_path']) {
} else {
    throw new \Exception;
}

```

People should be able to create several payments if the path same, but there is no way to crete several payments with different paths and itis Paypal's limitation. In this case we have to throw an exception.