Require email verification for sign up

[jackjohn7]

When a user signs up for an account, they shouldn't be able to sign into the account until the email address has been verified. Unverified accounts should be deleted in two weeks or less. This way, email typos aren't permanently wasting our precious DB space. This also prevents people from signing up with emails that aren't theirs.

There are several options for email senders. Twilio's SendGrid has a pretty adequate free tier that would allow us about 100 emails a day, so I think that will be perfectly adequate for the time being.

User should be notified on the front end when they signup that they need to verify their account

if they try to sign in, they need to be notified that they need to verify their email in order to sign in.