Easier email subscription for email users

[paskal]

The user who logged in with the email has to send and paste a token from the email to confirm the replies subscription.

The desired flow is confirmation of subscription without sending the token if the email is the same user logged in with. To make it live, we need to add a backend check for the address and some special flow for instant confirmation, either by returning something else than token after the first step and requiring the second API call as well as we do now or by just doing the confirmation in the first API call.