Emails / Unsubscribed users

1. Add a column in the main staff list, so we can identify who opted out of emails and contact them differently.

2. Allow users to change their email preferences in their profile. **At the moment, there is no option for them to re-subscribe once they've opted out.

We use the Bloomrang Volunteers Email function to send our mass mail, but also to send them crucial individualized information about their shift (like location, supervisor and shift confirmation module)