Add getChildren() signature in FedoraResource...

 - Implement it in FedoraResourceImpl.java
 - Expose the hierarchy levels through the IdentifierConverter and IdentifierTranslator on behalf of the getChildren() implementation.
 - Integrate the getChildren() method in FedoraResource to generate the hierarchy rdf triples for REST web UI.
 - Log the potential null children nodes and return as suggested.
 - Implement FedoraResource.getParent() for transparent hierarchy support.

Resolves: https://www.pivotaltracker.com/story/show/71941366
Fixing merging conflicts for rebase.
Enabled transparent hierarchy support for versions.
Enabled transparent hierarchy for locks.
Refactoring codes to enable transparent hierarchy to support function
like import, export, batch, and fixity etc.