2.x: support a deserialize-fn in the consumer configuration

[ghost]

wrap-body-with-msg-id does mostly the right thing - it puts on the prefix, but should treat the prefix entirely as a byte array (inclusive of the magic bits).

The publisher configuration has a serializer-fn to help with automatic serialization of published message bodies. Correspondingly, the consumer should have a deserialize function that allows the opposite action to take place.

At this time, split-body-and-msg-id stands in the way of that - because it always marshals the received message body into a string before stripping off the magic/msg-id/timestamp. It must do this without effecting the body's byte array and return the wrapped array unmodified (i.e. not transforming it to a string).

Kyle