Backdating existing chore doesn't change chore's last log date

Logging a chore sets the current date by default.

If you create a chore log, then edit it to a previous date, the chore will still show the later date.

TODO: Update ECA model to check if the chore log date is being changed and matches the chore's current log date. If it does, set it to the new log date value.

Also consider adding a last chore log reference field (instead?).