An event is a container for informations.
Whenever an object needs to send notifications to others it should implement
the EventSource class, and then send Event objects.
Events can be used for example as :

• mouse move event
• button click
• data update notification

return  EventSource who raised the event, never null.

Some events may be consumable.
Once consumed they should be ignored or discarded.
return  true if event consumable

return  true is event has been consumed.

Consume the event.

An event might have been trigger by another.
This method returns the original trigger event.
return  Event, can be null.