Changes to Threshold signing, round 2 — aggregate and return the signature

added the new optional request property client_commitments_all

added the new optional request property client_signature_shares_all

the response property key_id became required for the status 200

the response property message_digest became required for the status 200

the response property signature became required for the status 200

the response property signature_hex became required for the status 200

added the required property signatures to the response with the 200 status