Add endpoint and logic so appointment can be queried to pisa. A better implementation based on persistent storage (i.e. DB) should replace it in the future
Uses a proper KDF to extend the LSB of the txid (HKDF). Standardizes the representation of the keys / hashes in both sides (encrypt/decrypt deals with bytes now instead of string). Adds further logging.
Improves the dummy watcher logic. Sets a proper structure. Watcher can now check for potential matches and handle multiple appointments with the same locator (hash collisions).
