Facebook Real-Time Updates

Add support for real-time updates from Facebook. For details on Facebook's real-time updates, see https://developers.facebook.com/docs/reference/api/realtime/.

This issue covers adding API binding support for subscribing to a real-time feed at minimum, but also should include Spring MVC controller support for handling feed updates from Facebook. This can be either as a dedicated controller that generically handles all real-time updates and dispatches data to configured components (less complex, less flexible) or as a special controller base-class where the developer can write their own handling logic (more flexible, more complex).