Set the verified_on flag for IAddress through the REST API

IAddress.verified_on is how the core knows whether the registered address has been verified or not. Because Postorius supports registration via BrowserID, and by definition a BrowserID email address must be verified, we want to allow Postorius to set the verified_on field via the REST API.

This probably won't be a direct value setting. Instead, I think you want to POST true or false to .../<email address hidden>/verified and that will set IAddresses.verified_on to now() or to None.