"present but didn't pay" note

[dehnert]

Sometimes somebody is present but didn't pay, but in a way that's complicated and deserves some note (eg, this is arguably the correct way for gate to handle "they say they bought a subscription previously, but we don't have them, somebody please look" - Viz https://discord.com/channels/843577671085850644/1027013023405195334/1194453378013614331 ). With payments, gate can leave a note in the DB - maybe we should support this with non-payment too.