[REF] small cleanups on payment.create flow.

[REF] small cleanups on payment.create flow.

In the interests of keeping some momentum I added this small cleanup which does 3 things

1) uses the preferred function to get 'from_financial_account_id', 2 moves a line of code to get participantID
& 3 removes the conditionals around is_payment. This probably needs the most double checking but
I believe recordPartialPaymet used to be called from places other than Payment.create so
it may not have always been handling a payment - however it I can't see a case for it not be
is_payment now