Candlerb/error recovery

Fixes for #12 and #22

* Show the job ID and error message for instance creation failures
* If an instance creation fails, allow the application to be edited and
* resubmitted (or rejected)
* Make watcher more robust against exceptions

In essence: jobs in state PENDING, APPROVED or FAILED are all treated as if
they were "pending" and can be edited and resubmitted.