Staff role should not suppress reviewer emails

[bickelj]

Reviewer email notification for assigned application behavior corrected.

Fixes #3983

Test Steps

Set up a dummy email SMTP server or use file-based email.

• Update a user to be both Staff and Admin
• Assign that user to review an application/submission
• See emails go through to that user

[frjo]

We need some way to configure this. OTF uses Slack and their staff do not want duplicate info via e-mail.

I'm thinking a settings "STAFF_NOTIFICATION_METHOD" = email|slack|…