Better user-facing error messages when a Rodan job fails

Currently when a job fails, the only feedback the user gets is a Python error traceback. In addition to this traceback, there should be some kind of message that the job can pass back to the client, somehow, that the user can see.

For example - if the staff-finding job is capable of failing because it's given a blank image, there should be a check for that in the job itself, and when it throws an exception the message from the exception should be delivered back to the user in a friendlier and easier-to-read way than just the python stack trace. Hopefully this could lead to people being able to figure out why a job went wrong on their own even if they do not know how to interpret the error message.