Update API to 2014-06-17 and other minor improvements

I have updated the library to work with the Stripe API 2014-06-17. I have also added full refund support, with a refund service and list support. There is now a Refund method on StripeCharge entities also. All changes are backwards compatible and should have tests.

I have also changed some tests so that they get the currency from AppSettings. Also StripeEventListOptions now inherits from StripeListOptions.

No version numbers have been updated except the API version in StripeConfiguration.