Hierarchy children

https://www.pivotaltracker.com/s/projects/684825/stories/71611298
@awoods:  I think the getChildren() method should be working as expected, and we should in a better position with the transparent hierarchy approach now. I also added a static getChildren() method in FedoraResourceImpl.java for convenient use, and integrated it to the HierarchyRdfContext.java for the REST web UI display so that you can evaluate the approach without any delays.