Payments appear as "KillBill Charge" on customers' bank statements

[GregOriol]

Since version 7.x of the plugin, the payments appear as "KillBill Charge" on customer's bank statements, this is a critical issue!

Many problems here:

1. the value sent for the statement descriptor is available as a property to be changed, but it is not documented!!
2. the value defaults to "KillBill Charge" if not set, and it is a really bad choice, customer have absolutely no idea what KillBill is
3. this default value is sent while the parameter is optional, and it overrides the setting defined on Stripe's account/dashboard which should used as the default (if not overridden by the property)

A few possible solution:

1. document this property (and the others) and their default values
2. don't send the statement_descriptor field if the property is not explicitly set, which will fallback on the one defined on the Stripe account/dashboard
3. maybe instead of statement_descriptor, it would be better to use statement_descriptor_suffix, which appends details to the value defined on the Stripe account/dashboard, and is here to give the customer a better idea of what the statement they see on their bank's side is for (invoice number, ...) => but that wouldn't be a property, it should be some reference from the Invoice, though it must be 2 to 10 characters and I don't think we have such a value available