first class support for requesting a new key

[vilmibm]

by far the most common help desk issue is "help i need a new key." there isn't a good way to solve for this without some manual intervention, but we should take a similar approach as we do to signups:

• user fills out a form that validates they are submitting a valid public key
• on form submit,
  • KeyRequestSignup is created
  • admin app sends an email verification

Requests are marked as "unverified" until the email address is verified; at that point, an admin can approve and process the request.