Improve data serialization for JSON inputs

[cankisagun]

Enclave data is serialized for sealing/unsealing using JSON format, which is highly inefficient in terms of space. This should be improved using a binary format such as CBOR. The correct library serde-cbor that is SGX compatible should be identified and used, the code adjusted to use that. Data is JSON_serialized in [enclave/src/data.rs] in the first line of create_sealeddata_for_serializable(), and later deserialized in the last line of recover_sealeddata_for_serializable().