Set up Mailgun

[tiffz]

We will want to send emails to users for:

• Initial interest building period. We should have some sort of mailing list that we create and send people updates on during our ~1 month interest building period before launch.
• Verifying email addresses. Note, this should not be required to login but there should be an annoying thing that tells you to verify your email (and lets you change your email if it's wrong/resend if it got missed) if you haven't yet.
• Forgotten password feature. Email people some sort of secret link to reset their password. (we'll have to think some about how to design this in a reasonably secure way)

[tiffz]

This is better tracked by #117 and #31

Edit: Also Mailgun is "Set up"