[BACKLOG-248] Write extension point plugin producing guava bus events
	- created kettle-monitoring-plugin as the first step ( read: entry-point ) to PDI monitoring story
	- uses PDI Extension Point Plugins mechanism ( see http://wiki.pentaho.com/display/EAI/PDI+Extension+Point+Plugins )	- uses event bus plugin work @ https://github.com/pentaho/pentaho-platform/tree/monitoring
	- when the PDI Extension Point Plugins mechanism is triggered at a specific event, an Event object is built and posted to the eventbus, where an EventSubscriber for this type of event has been previously subscribed
Merge pull request #679 from pedrofvteixeira/monitoring

[BACKLOG-248] Write extension point plugin producing guava bus events