Add @job_result decorator wherever applicable

[vineetbansal]

The @job_result decorator is used for the job_query endpoint, and intercepts the logic to show a generic error page if there's an error (handled or unhandled). This should be used for all endpoints where it makes sense.

We can also modify the base template to handle the PENDING job status, and thus simplify the templates that derive from it, which can then assume that the job ran successfully.