Add fraud reporting methods

r? @cosn 

Add methods for reporting charges as safe/fraudulent and including reasons in refunds.
OK, so if we're not allowing the "StripeReported" in the params, can we just move this as "FraudReport" on the `ChargeParams`? Seems cleaner than having to create a new struct (`FraudDetails`) to set a single property. 

This also means that we can now have `FraudDetails` as its own struct and not overload the params