Allow resending verification emails

Created by: ryanslade

We need to add a graphQL mutation that allows us to resend a verification email:

resendVerificationEmail(user: ID!, email: String!): EmptyResponse!

It is a noop if:

• The email is already verified

It is an error if:

• User doesn't exist
• The user hasn't added the supplied email

We should also limit how often we can resend, perhaps initially to once every 5 minutes. We already store the last time an email was sent in the last_verification_sent_at column.