Add repl feedback to clj-frontend using EventBus

Subscribe to EventBus events display results in the repl while a
workflow is running.  The current implementation subscribes to all
events.  A future implementation may just subscribe to the superclass
and respond differenty to each event type in order to minimize the
interop code.
Move EventBus code into clj-frontend-utils
Add tests and cleanup for clj-frontend/EventBus

Add a test to make sure that clj-frontend with EventBus is working.

Clean up the code a bit and add some comments.
clj-frontend/run-workflow run automatially

Make :auto true a default in clj-frontend/run-workflow.  The :preview
true option trumps :auto true, so we can safely use :preview true to get
a preview without the workflow running.
Merge pull request #124 from morrifeldman/feature/clj-frontend-event

Add repl feedback to clj-frontend using EventBus