Refine admin delete confirmation

[rachelekm]

When deleting users through the Django admin there is a confirmation prompt clarifying the user to be deleted as well as their related blog posts (articles where they are the author):

However, recently staff were clearing out outdated admin users and accidentally deleted blog posts (published and draft versions) that they wanted to persist even though they were related to the to-be-deleted users. It would be worth re-visiting this confirmation page to either update the language or design (or at least ask Nick what he thinks) to make action side effects more clear. See slack discussion.