Add pipeline edit modal with parallelism control

[jbeisen]

Add an "Edit" button on the job details page that opens up a modal. The modal contains a form that can be used to change the parallelism.

Resolves: #74

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This is a work in progress. Still to do:

• add more validation to the form
• indicate on the job details page that the pipeline is restarting
  I guess it already does this?
• maybe change the design of the restart warning?

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The modal:

If you change the parallelism value:

[mwylde]

This is great!

The only issue I noticed is that if you edit the parallelism and hit cancel, re-opening the modal shows the edited parallelism rather than the actual current parallelism (in other words, cancel doesn't reset the state of the modal).

[mwylde]

Should this be a number input?

[jbeisen]

Yes, done. I had to manually set the background color, though. Maybe there's a bug with the dark theme.

[mwylde]

Ship it!