Provide translation for the price component label

The price component label should be passed to the t() function.

We need to modify the hook_commerce_price_component_type_info in this way:

/**
 * Implements hook_commerce_price_component_type_info().
 */
function commerce_coupon_commerce_price_component_type_info() {
  $components = array();

  // Add a price component type for each tax rate that specifies it.
  foreach (commerce_coupon_get_types() as $type => $coupon_type) {
    $components['commerce_coupon_' . $type] = array(
      'title' => $coupon_type->label,
      'display_title' => t($coupon_type->label),
    );
  }

  return $components;
}