Modify REST-API call "verify" - provide interface for postfix smtp-filter

As described in #101 , the verify call needs to be extended and should check if the local dApp has verifiable local data which have a valid permission (correct signatures) inside the blockchain.

In case the local database doesn't hold nameId and or public_key of Alice, we must either purely rely on the local data or find a way to gather or save public_key of Alice in order to decrypt the signatures inside Doichain. Please lets further discuss this issue here!

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