Logic error with deactivating people

[lroellin]

The following process leads to a bug where you can't settle up the group anymore. We may need to think again how we handle deactivating users.

My proposal would be that you can't deactivate users when they're still in a transaction. That however may lead to users not using that feature since it's cumbersome or even impossible, but at least it's not wrong anymore.

Reproducible bug description:

1. Create a new group
2. Create two people, Alice and Daniel
3. Create an expense, Payer Alice, Profiteer Daniel (only), amount irrelevant (e.g. 20€)
4. Suggest payments, create a compensation from Daniel to Alice over that amount (e.g. 20€)
5. Deactivate Daniel
6. Delete the compensation you just made
7. Suggest payments again, it suggests these 20€ from Daniel to Alice again
8. Create a compensation from Daniel to Alice
9. Receive "PAYER_INACTIVE"