Response Validation & Processing

- [x] Add Response Precondition checking
- [x] Add Response signature verification
- [x] Add Response Validation
- [X] Add Response Assertion Decryption
- [x] Add Response Assertion Validation
- [x] Add Response Assertion Transformers
- [ ] Test all the things
`$collection->getSoleElement()`? Can't quite figure out what a good name for such a method would be....