Shared Keys for Private Exchanges

Breaking Changes

Significant changes as we mature #B:

1. Now uses Elliptic Curve Diffe-Hellman shared key instead of Fernet (#81), changing how UTXQ/MTXQ are encrypted. The old encrypted data will not be migrated.

2. In oder to remove the user constraint of managing asset prime number (values) (#87), we've changed the address scheme. Refer to Address Scheme

General:

Core focus is on removing the fernet key as THE encryption/decryption key for exchange data in the PoC and move on to a shared key PoC solution and optimizing Asset unique value representation (prime numbers).

Enhancements:

#78
#81
#87

Fixes:

#83
#85
#86