Refactoring and improved error handling Go/cpp code following #501

[bvavala]

A lot of code has to be refactored both in Go and in the enclave.
List of tasks:

• go pdo crypto in separate module (and cleanup of obsolete internal/utils/crypto.go) to make mock_enclave.go also work with new message format, see comment support for digital signatures + integration tests work (again) #501 (comment) and issue mock_ecc doesn't build #513
• use of go pdo crypto also for hash, see comment support for digital signatures + integration tests work (again) #501 (comment)
• error handling of state functions (they are void, should be bool)
• state values from string to binary (see comment support for digital signatures + integration tests work (again) #501 (comment))