Since a deployed TaskDef is by nature incomplete (doesn't have an id, versionId, nor deploymentDate),
we here pass a TaskDefParser instance, which will somehow load our TaskDef definition
(from an xml file for instance), and pass it on for actual deployment.
Retrieves the pending tasks assigned to an assignee
(or a group/pool of actors TODO ?), so that a specific actor can see
what tasks he could do if he's bored.
Creates a new instance of a given task definition (the last deployed TaskDef with
the given name), reported by the given userid, assigns it a specific id, name and description.
A simple object passed to TaskAction which exposes the event
which triggered this TaskAction and the concerned TaskInstance;
it also exposes a couple of lifecycle methods for the current TaskInstance.