feature: provisional submit [try mode]

[mildred]

Sometimes, especially when setting up an account, I want to try submitting multiple transactions and look at the outcome (see if the account total is correct, ...) In case of error, I'd like to revert the submission, edit the item, and try again.

Perhaps a global try mode toggle could be added, and when enabled all submissions could be undone to allow edits and submitting again. Only the items submitted during try mode enabled could be undone. When try mode is disabled, all submits should be made permanent.