Improve performance of ConceptService.getConceptsByMapping

More and more, form entry frameworks (specifically htmlformentry) and other metadata configuration mechanisms are promoting the use of concept reference terms to refer to concepts.  We have some forms that make over 1000 concept look-ups, to get information to construct and populate a form with the appropriate questions, answers, and other associated concept metadata.  These forms are taking a long time to load, and we have traced the biggest culprit down to loading Concepts by mapping.

This ticket aims to improve the performance of looking up Concepts by Mapping by refactoring the DAO method to utilize a Lucene index rather than doing a direct query of the database using HQL.