experimenting with accessign the SKOSManager and concepts by using the OWLOntology manager, which will make integration easier
Experimenting (unsuccessfully) with using HermiT as a reasoner for SKOSReasoner, to get the broader/narrower hierarchies/
Experimenting with using Pellet as the OWL reasoner for use with the SKOSReasoner, still not working

(committed for future reference)
As a temporary measure, manually determine the narrower and broader terms by extracting the annotations

This is been added to a wrapping class, with the aim to eventually
replace this internals with code using the SKOSReasoner.
Detect whether an ontology is infact a SKOS document, by the inclusion of #Concept class in the signature
Added method to SKOS hierarchy reader to get the top concepts
First raw version of opening a SKOS file and having its broader/narrower hierarchy displayed in the hierarchy panel
Given SKOS its own icon in the hierarchy tree
Some refactoring of JTree extension for Class and SKOS tree, to make more OO, which should help with the further integration of SKOS
Fixed test
The SKOS hierarchy tree now returns the selected entity as a converted skosconcept to the owlentity.

Also, some additional refactoring to share functionality for getting the
ontology a particular entity belongs to (to allow us to detect a SKOS
document later on).