fixes #64
-- upgraded to AKKA 2.3.4
-- upgraded journal tests
-- updated build dependencies
-- migrated command sourcing tests to use PersistentActor
-- renamed all references of processorId to persistenceId
-- removed tests for single delete of messages since that method call is deprecated and no longer required.
Merge pull request #65 from ddevore/wip-upgrade-to-akka-2.3.4

fixes #64