Feature/223 ensure interface compliance improve implementation

[PropzSaladaz]

Description

These changes refer to improving current libBLS codebase regarding:

1. Usage of TEWrapper classes isntead of libff primitive types. Implementation of new classes: TEbase (has base fields from which any other TEWrapper inherits from), and TEDecryptionShare.
2. Separation of logic from data - Threshold Encryption logic is now all contained within a single ThresholdEncryption class, instead of being 'scattered' across several different TEWrappers (TEPublicKey, TEPrivateKeyShare, TEDecryptSet, ... ). Easier for end-users to work with the library this way.
   2.1 - Added new functionality to validate a cyphertext against its decyphered plaintext.
3. Fix AES cipher - It was currently allocating incorrect number of bytes for the output cipher vector. Some messages (with length < 38) were resulting in memory-related errors. It was also allocating more than needed amount of bytes for Initialization Vector (IV).
4. Change the base flow of encryption/decryption. Now calling encrypt will cipher the plaintext using an AES key by default, and only the AES key will run the threshold encryption stages (decryptShare, VerifyShare, ...)
5. Serialization of the U field of ciphertext is sent to sgx as hexadecimal instead of double comma-separated string.

Tests

• Most of the tests were updated to use the new Wrappers
• Some tests were slightly changed to test different message lengths
• Some tests were removed - No longer needed due to the changes made
• Updated te_sample_sgx.cpp to use batching when sending decryption requests to sgx
• Added a test to test the added cyphertext validation functionality (stress out invalid messages from being accepted)

Fixes #223