Escalate reviews for apps with prerelease permissions (bug 1036921)

https://bugzilla.mozilla.org/show_bug.cgi?id=1036921

Depends on mozilla/app-validator#33.

This will escalate the review of new and updated packaged apps if they use any of the prerelease permissions that are switching to privileged from certified.
I don't suppose it matters a great deal, but you can use the developer who uploaded the version as the user to avoid using nobody.