Refactor CBOR (de)-serialization

[nmdanny]

• Find a more generic way of deserializing Keymappable objects that does not rely on intermediate conversion to a CBOR value
  (similar to how the Serializer is implemented)
• Find a nicer way of sorting CBOR maps without converting to intermediate CBOR values
• Alternatively, find an alternative CBOR library that already does some of this.
  minicbor seemed almost fitting, except that it forces you to you use integer keys for all structs,
  and I need string keys for structs that aren't top level request/response objects.