Merged netwk/ and coordinator/ into coordinator/

This was done because the netwk/ package no longer has any network
specific code in it (apart from the tests). The listener and responder
types were really just part of the message coordination system and it
made no sense to have them in separate packages.

There is only one exported function in coordinator Coordinate(...). This
significantly reduces the surface area that was previously exposed by
the netwk package.

Small changes include:

Split the dispatcher into its own file dispatch.go

Changed the Listener and Responder types to stdListener and
stdResponder. This makes both types private and differentiates them from
the listener and responder interfaces found inside coordinator.go. An
attempt was made to remove these interfaces and use the raw types
directly but this made testing difficult (specifically the tests found
in tdispatch_test.go).