WebPay: modify the currency unit in JPY from yen (1) to sen (1/100).
WebPay: update a test API key.
WebPay: add unit tests to check the currency unit.
WebPay: modify refund method to support the new currency unit in JPY.
WebPay: add tests to modify currency unit in JPY from yen to sen.
Merge pull request #822 from keikubo/webpay_currency_unit

Webpay: modify currency unit from yen (1) to sen (1/100) in JPY