revoke permission specification and compromised privateKeys approach

when a DOI (permission) was given, so far it stays with the ownership of Bob (email provider), which is correct and should NOT be changed.

in case Peter (the recipient) wants to revoke a permission he should browse his permission on his responsible Doichain dApp (Bob) and revoke the permission for a sender (Alice) there.

As soon as Bob revokes he should identically inform Alice about the revocation as he did for the confirmation. Alice now deletes (or better flag revoked = true) her local records of Peter automatically.

Please see https://bounties.doichain.org/ how to apply for Doichain bounties.