* Add fbemitter, keep flow passing
* Begin support for event emitter
- Adds emitter to navigation prop
- Emits top level onAction event
- stub getChildEventSubscriber for child events
* Support navigationState.isNavigating
* Focus and blur events starting to work
- Navigation completion action wired up
- Event chaining logic built in getChildEventSubscriber
- Renamed onAction evt to ‘action’
* Wrap up events progress and testing
* Rename to isTransitioning and COMPLETE_TRANSITION
* rm accidental dependency
* Suppoert event payload type
