Ignore .DS_Store
Minor refactoring

* DomainEvent - added eventType()
* DomainEventSubscriber - added handlesEventType(), changed
subscribedEventType() to listHandledEventTypes()
* DomainEventPublisher - changed subscribers key to spl_object_hash of
subscriber
* Updated DomainEventPublisherTest
Add SubscriberQueue
Refactor to use internal, managed queue
Add SubscriberQueue to DomainEventPublisher
Rename DomainEvent to Event
Rename DomainEventPublisher to EventPublisher
Rename DomainEventSubscriber to EventHandler
Rename SubscriberQueue to HandlerQueue
Update StoredEvent for Event::eventType()