hledger-web 1.50 doesn't follow own openapi spec

[aragaer]

The #2395 had removed aibalance, aebalance and anumpostings fields from Account class and from its toJSON representation. However all these three fields are declared as required in the current openapi.yaml.

Also the aboring field is still present in the class, but not in the json representation and it's also a required field according to the schema.