Tasks can have actions associated with them.  There are 4 standard event types defined 
    for tasks: task-create, 
    task-assign, task-start and task-end.
task-create is fired when a task instance is created.
task-assign is fired when a task instance is being assigned.  
    Note that in actions that are executed on this event, you can access the previous 
    actor with executionContext.getTaskInstance().getPreviousActorId();
    
task-start is fired when TaskInstance.start()
    is called.  This can be used to indicate that the user is actually starting to work on this 
    task instance.  Starting a task is optional.
task-end is fired when TaskInstance.end(...)
    is called.  This marks the completion of the task.  If the task is related to a process 
    execution, this call might trigger the resuming of the process execution.
    
Since tasks can have events and actions associated with them, also exception handlers can be specified on a task. For more information about exception handling, see the section called “Exception handling”.