Handle user closing panel while creating job/job definition unsuccessfully

[JasonWeill]

Problem

From @ellisonbg 's comment on #186: "What happens if the user closes the panel while the job is being created and job creation fails? I guess there won't be any record of that job?"

Proposed Solution

Provide feedback to the user the next time they open the Notebook Jobs panel (in create or list mode) about previous job creations having failed.