Improve enclave error handling - Internal Enigma

[cankisagun]

Error handling needs much improvement, as most functions inside the enclave will return success regardless of whether the fail or succeed. This obviously makes it hard to debug and troubleshoot. The developer team at Enigma is working on the right infrastructure for error handling with enigmampc/EnigmaBlockchain. Once that work is completed, it should be straightforward to be ported to this repo.