Changes Interactors to accept Parcels, not Messages.

Details:
* Big downside of Interactors only accepting messages is that tracking
  information is lost if said Interactors spin off new requests
  based on the original inbound request. Such as the case of
  Scatter-Gather pattern, subsequent UUID tracking is broken to the
  origin.
* With this change, the Interactor has access to the full request
  parcel to be able to pass on the tracking UUIDs along with
  subsequent request parcels.
* The downside is that this added exposure may make it tempting
  for Interactors to use header information as part of their
  business logic. This is FROWNED UPON as we should only look
  in the message itself as input to the business logic processing.