make ApplicationFee.refunds a list object instead of array
Revert "make ApplicationFee.refunds a list object instead of array"

This reverts commit 3bc178861feedbe90169d43625c6bd92baf4d170.
1. removed refs to id builtin in favor of id_
2. using params.pop instead of params.get
- prevent id key from residing in params
- avoid overriding id builtin
- allow backwards compatibility; id, id_
3. adding APIResource compatibility integration test
4. Testing ListObject.retrieve with None values for id/id_