US16295 Payload and Message Factory

Create a payload factory whose sole responsibility will be to construct
new payloads via a configuration file.

Create a bidirectional message factory that will use the payload factory
to create Http request/reply payloads.

Create a payload map that payloads may use to get a configured concrete
type for an abstract type needed by the payload - e.g. for payloads to
build sub-payload types.