Decouple parsing from results objects to unmarshallers

Page results objects such as BankRecordResults are now POJOs
and the logic is transfered to unmarshall objects.
Removed page results objects from inheriting from NeopetsPageResults.
Instead, these objects will have a PageStatus member.
Make exceptions in the Bank model to checked
Decouple error handling to exception handlers

Change exception in the Bank model to checked exceptions.