TRUNK-3840: Refactoring code to display retired set member

https://issues.openmrs.org/browse/TRUNK-3840

Refactored concept.jsp; removed repeated code.
Add code to ConceptSet.java to factor in retired concepts while sorting
Added unit test for new behavior

Updated concept.jsp view and ConceptFormController
All the code in this closed can be replaces with  just:
OpenmrsUtil.compareWithNullAsLowest(concept.getSortedWeight(), cs.getSortedWeight())