Signature conditions for tests [#3206]
Closes #3206 (closed). Overhauls the test harness's condition support to add support to conditions on signatures and messages produced by signatures (e.g. authority signatures). Updates the ID method of the CreditPayment message type to use the transaction principal as the account instead of the payer, to align with routing. The credit payment is sent to the principal, therefore you must query the principal's partition to get the message's status, therefore the message's ID should include the principal, not the payer.
Changelog: test