Add an 'embedded' group for channel-based client/coordinator

Needed to test some external Metafora usage, and wanted to add unit tests which did not rely on external communication.

Interested in further ideas/input.
Hm, Run should block until Shutdown is called... I think you just want to call Shutdown() where you sleep and close the channel. If all the chans are synchronous I *think* the tasks will always be handled by the Consumer before the Shutdown is processed. If they're not, that's ... interesting.