Handle additional bodyParser errors

[matthew-white]

If the size of a JSON request body exceeds the bodyParser limit in Backend, then bodyParser will throw an error with a status property of 413. However, Backend will then return a 500 error, not a 413. The error has the message, "Completely unhandled exception: request entity too large". I think it would be ideal for Backend to return a 413 Problem in this case. (See getodk/central-backend#446 for some more details about this error.)

We already handle bodyParser errors of type entity.parse.failed. Given that, I think we could do something similar for errors of type entity.too.large. It would probably be useful to also take a look at the list of bodyParser errors to see if there are others to account for. (Is there a generic way to handle any bodyParser error?)