bundle2: produce a bundle2 reply We do not know yet what kind of data future features and extensions will need to exchange. To handle that, bundle2 allows to send arbitrary content to the server. As a consequence, we need to be able to reply arbitrary content to the client. And, we can use bundle2 to transmit those arbitrary data. When a client will push a bundle2 to the server, the server will reply with a bundle2 itself. This changeset installs the first stone of this logic and test it.