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
@wluyima not sure why I didn't notice this the first time, but the sort logic sorts the weights in ascending order. Not sure what will break if I reverse the order, since this is how it has been working, so I'll leave it as is.