Refactor and add some tests for CampaignDetails

Created by: sqs

See commit messages.

There is no behavior change except one thing:

• The campaign job status used to be shown when the campaign type was non-manual. Now it is shown if pending + completed jobs is non-zero. I think this is equivalent. Let me know if I am wrong. (This change just lets us avoid passing another prop to the new CampaignStatus component.)