Update tests to use StripeCurrency AppSetting for currency.
Update more test data to use AppSetting currency.
Update last few fixed currency occurances to use AppSettings.
StripeEventListOptions now inherits from StripeListOptions

This allows the use of other list options.
Update Library to work with API version 2014-05-19

- Update Transfer entity, changed "account" JsonProperty to "bank_account"
Update API support to 2014-06-17

- Rename "type" on card entity to "brand" - but kept backwards compatibility.
- Add StripeRefundService class, StripeRefundCreateOption class, StripeRefund entity and StripeRefundList entity.
- Update old Refund method in StripeChargeService to use StripeRefundService, which is attributed as obsolete.
- Add tests for new refund classes.
- Add refund list to charge entity.
- Add refund method to charge entity, for convenience.
- Add refund url to Urls class.
More refund tests