Change picture for Bundesdruckerei-Wallet

[LevinJac]

At the moment our Bundesdruckerei actor uses the same picture as our Vendor. We should create some sort of Logo for the Bundesdruckerei and put it in the repos controller\public\ directory.

Then we can update our Bundesdruckerei picture by linking to it in the AcaPy-Swagger UIs PUT multitenancy/wallet/{wallet-id} option.
E.g. "image_url": "http://id.epcat.de/api/public/bundesdruckerei.png"