Fix compatibility with maven artifacts

* make generateUndoundJar task accessible from project config
example : 
artifacts{
	archives generateUnboundTask
}

* add classifier to be able to upload generated jar into a repo
Where is the problem if the archive is not generated ?

Following build lifecycle (http://www.gradle.org/docs/current/userguide/build_lifecycle.html)
* the task is created @ initialization time (with the change)
* During configuration phase, the task is available to configuration other tasks (like artifacts)
* After config the task is disabled by "onlyIf" if unboundJarName is not set
* So the archiveName is never set because closure is not executed @ execution time