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.
is the change from self.request.amo_user to self.request_user deliberate?