Set up email

[alexgleason]

Currently, email is not enabled on projecttier.org.

1. This prevents "I forgot my password" from working - it cannot send you the recovery email.
2. This prevents website errors from being reported to us.

Adding this would make #62 less bad, since we'd be notified immediately when a user tries to visit a broken link, rather than learning too late that it's happening.

I've set up an account on Postmark for TIER to send emails, but we need to verify it with the domain name before we can enable it. Then we'll just need to update the site settings to use Postmark's email info.