Verify email address on register

[lebaaar]

When user registers, send an email to the entered email. Code expires in 1 hour

TODO:

• Create an email template (with SendGrid), have consistent styling in emails (ask @lebaaar)
• Send email on register with a random generated 6 digit code. Store code in DB, expiration is 1 hour. If user doesn't verify email, delete the user entry from DB? So the email isn't taken forever. Check how other apps do this
• On frontend - add enter code screen. Even after login, in any browser the user should be sent to enter code screen