XD-1351 replaced Plugin.preprocessSharedContext with ApplicationListener

- AbstractPlugin implements Ordered
- Removed preprocessSharedContext() from Plugin.  
- Added a new SharedContextInitializer interface that extends ApplicationListener<ApplicationPreparedEvent> ,Ordered 
- Implemented a MessageBusInitializer to initialize the messageBus.
- Moved message-bus.xml and related config out of plugins directory, into listeners
- Modified ModuleDeployer.onInit()
- Refactored tests