Description of problem:
Each user can only validate a single email address, and email address changes are not visible through the UI until they are successfully validated.

The UI should:

 - show email addresses that are awaiting validation.
 - show email addresses for which all validation links have expired
 - allow users to have validation emails re-sent (this could expire any previous validation links for the address).
 - show previously validated email addresses.
 - allow users to set any validated email address as their contact address.
 - allow users to delete any email address that is not their primary contact address (for non-validated email addresses, this could expire all validation links for the address).

Other thoughts:

 - the target page of validation links could offer to use the validated address as the contact address.
 - users trying to add an address that is already validated for themselves would be asked if they want to use it as their primary address.
 - users trying to add an address that is in their validation queue would be offered to re-send validation email.
 - email addresses in validation queue of other users should not be taken into account for detecting duplicate emails (to prevent accidental or purposeful locking-up of others' email addresses).