Hierarchy children

@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.
It's strange that my earlier commits are popping out along with this PR, but only the last two are the changes I made this time. I pulled the hierarchy branch from upstream to reinitiate my local repo yesterday when I found some confections after a pull from upstream. Please let me know if anything that I can do to make the merging easier. Thanks.
https://www.pivotaltracker.com/s/projects/684825/stories/71611298