Add better testing support

[ryanmoelter]

• Make Journey.navigator @VisibleForTesting so we can access it in tests for verification
• Make transition methods public, move from LifecycleStateMachine to extension functions on LifecycleAware
  • This makes it easier to get LifecycleAware objects into the right state when testing them
  • Also updated some sample tests to use this method instead of calling lifecycle events directly
• Detach LifecycleAware objects attached using by attachFieldToLifecycle when field is set (usually in tests)
  • This means that the original implementations don't get lifecycle events when we use fakes/mocks in tests